A single dose pouch reads as the cheapest line on a fill quotation right up to the point where the component numbers arrive. The laminate is bought by the roll against a printed minimum that rarely matches the volume a launch plan was built around, the artwork is booked into a print slot weeks before the formula is signed off because cylinder & plate lead times sit ahead of everything else, & the dose size then fixes the case count, the freight volume & the price per millilitre the marketing budget assumed. A flat sachet & a narrow stick pack do not run on the same machine either: they use different forming collars, different registration systems, different seal tooling & different tolerances on delivered weight. The format therefore has to be decided while it is still free to decide, which is earlier than most briefs do it.
This piece covers what a laminate is built from, how water vapour transmission & oxygen transmission are specified against a real shelf life rather than a marketing one, why the seal window is narrower than a specification usually implies, what a viscous formula does to delivered accuracy inside a narrow tube, where a stick pack differs from a flat sachet beyond the shape of the unit, which compatibility work has to be finished before artwork is committed, how a change of dose changes the unit cost on both the film & the filling side, & the sequence of sampling rounds that keeps those decisions reversible for as long as possible. It is written for the person who signs the specification rather than for the person who runs the machine.
Why the film is chosen before the formula is frozen
There is a temptation to develop the formula, approve the sample, & then ask what the pack should be. For a single dose format that order costs money twice. The barrier requirement comes from the formula: a High water activity emulsion in a thin film loses water through the laminate rather than through the seal, & the measured consequence is a product that thickens, darkens & eventually fails its own viscosity specification in month nine of a two year claim. Knowing that early changes the laminate choice, & changing the laminate after artwork has been printed onto a different structure means reprinting.
The reverse constraint is just as real. Once a dose size is picked, the surface area to volume ratio of the unit is fixed & so is the rate at which anything crosses the film. Going from ten millilitres to five millilitres roughly doubles that ratio per unit of product, which is why a small dose of a delicate formula can be harder to stabilise than a large one of the same material. The two decisions have to be taken together or neither can be optimised, & in practice this is the first argument a factory should have with a buyer.
The commercial argument points the same way. A printed laminate carries a minimum order, a cylinder cost if the print is gravure, a plate or digital setup if it is flexographic, & a lead time that does not compress because a marketing calendar changed. A brand that freezes the dose before it has a formula it likes is buying film against a guess, & the film is the one component in a single dose programme that cannot be substituted at short notice.
What a laminate is actually made of
A cosmetic single dose pouch is a multi layer structure, & each layer has one job it does well & one it does badly. The outer layer takes the print & the abrasion of distribution: polyester (PET) is common because it holds ink well, resists scuffing & gives the structure dimensional stability through the heat of sealing; oriented polyamide (OPA or nylon) is chosen where puncture resistance matters, such as an angular unit packed tightly in a carton; paper appears where a natural look is wanted & takes a matte varnish but contributes very little barrier of its own.
The barrier layer is the one doing the invisible work. Aluminium foil in the six to twelve micron range is close to a total barrier against water vapour, oxygen & light, which is why it appears in structures holding anything with an unsaturated oil phase, a retinoid, ascorbic acid or a volatile fragrance top note. Metallised PET gives a lower but still useful barrier at a lower cost & with better flex crack resistance; EVOH (ethylene vinyl alcohol copolymer) gives an excellent oxygen barrier only while it stays dry, because its performance falls off sharply once it absorbs moisture, so it is normally buried inside the structure away from the product & the environment; PVDC coatings sit somewhere between.
The inner layer is the sealant & the contact surface. Polyethylene is the default, with metallocene grades giving a lower seal initiation temperature, better hot tack & better seal-through-contamination behaviour, which matters enormously when the product being packed is an oil or a surfactant solution that will be sitting in the seal area at the moment the jaws close. Cast polypropylene is used where the pack will see a retort or a hot fill. The inner layer also decides compatibility, because it is the polymer the formula actually touches for the whole of its shelf life.
Then come the invisible members of the structure: the adhesive or extrusion tie layer holding it together, or a corona discharge priming step that lets ink stick to the outer face, the slip & antiblock additives that let the film run over the machine, & any coating applied for a matte or soft touch effect. Each one is a migration candidate & a compatibility question, which is why a laminate datasheet alone is not enough & the full structure declaration has to be requested.
Water vapour transmission & how shelf life is really set
Water vapour transmission rate is quoted in grams per square metre per day at a stated temperature & relative humidity, & the conditions are not interchangeable between suppliers. A figure taken at 38 °C & 90% relative humidity & a figure taken at 23 °C & 50% relative humidity are not two measurements of one property; they can differ by a factor of several. The first question to ask about any WVTR number on a datasheet is therefore which conditions produced it, & the second is whether the number was measured on the flat laminate or predicted from the individual layers, because predicted values assume a perfect bond & a perfect foil.
The useful arithmetic takes the transmission rate, multiplies by the surface area of the unit & divides by the fill weight, which gives the percentage of water the product can lose per unit time in a stated climate. Across a twenty four month claim that number is not small for anything below about eight grams per square metre per day in a small dose. The practical approach is to set a maximum acceptable weight loss over the claim period, work backwards to the transmission rate that delivers it for the chosen geometry, & then let the supplier propose the cheapest structure that meets the derived figure rather than asking for "good barrier".
Flex cracking is what turns a good datasheet into a failing pouch. A foil layer develops pinholes & then cracks when the laminate is creased or flexed repeatedly, which is exactly what happens in a carton rattling around a pallet on its way to a distribution centre; once the foil is cracked the barrier collapses locally & the measured transmission rate of the intact sheet becomes irrelevant. Testing the creased structure rather than the flat one, & including a real or simulated transit cycle in the stability programme for foil based pouches, is the step that catches this before shipment rather than after.
Weight loss is not only a formula problem. A unit that loses five percent of its water still contains the right amount of everything else, but it now contains a higher concentration of surfactant, salt or preservative than the specification allows, it may no longer meet its declared content on pack, & its viscosity has drifted far enough that a customer squeezes out something visibly different from what they bought before. Content declarations & minimum fill are therefore tied to barrier choice, not just to filler accuracy.
Oxygen, light & the barrier that is usually missed
Oxygen transmission matters less often in cosmetic work than water does, & when it matters it tends to matter absolutely rather than partially. An unsaturated plant oil goes rancid & develops a sharp odour; a fragrance loses its top notes & the customer notices the product smells different from the tester; ascorbic acid oxidises & browns; certain antioxidant packages are consumed faster than expected & everything downstream gets shorter. In each of those situations there is no partial failure to negotiate about, & the fix is a foil or metallised layer rather than a thicker sealant.
Light is the transmission route nobody quotes. A transparent or translucent structure lets visible & ultraviolet radiation reach the product for the whole of the shelf life, which combined with oxygen ingress accelerates colour change in anything containing a botanical extract, a dye, or a pearl suspension. The usual answer is not necessarily foil: an opaque white structure, a paper outer layer or a heavy white ink coverage can do the job at lower cost. A brand that wants transparency for aesthetically driven reasons & also wants a two year claim on an oxygen sensitive formula has asked for two things that pull against each other, & the honest answer is usually to change the claim rather than the film.
Volatile loss outwards is the same problem in reverse & it is frequently the reason a fragrance product smells wrong in the unit even though nothing entered it. Fragrance components are small molecules that migrate through polyethylene comfortably; a HDPE sealant holds them better than LDPE, & a foil layer holds them almost completely. Where a scented product is being packed, the arrow pointing outwards deserves as much attention as the arrows pointing in.
Then there is the interaction nobody models: the product itself can attack the laminate. A high level of a light ester or a hydrocarbon solvent can swell a polyethylene sealant, extract its slip additives, cause delamination at the adhesive interface, or produce a visible clouding in the film. This is why compatibility work uses the actual formula rather than a water based placebo, & why it runs at elevated temperature to shorten the feedback loop.
The seal window: temperature, dwell & pressure together
A heat seal is made by bringing the two inner faces to a temperature at which the sealant melts, holding them together for long enough for the polymer chains to interdiffuse across the interface, & then cooling the joint under pressure so the melt does not relax apart. That produces a window rather than a set point: too cool & the sealant never reaches its seal initiation temperature, giving a joint that looks closed & peels with finger pressure; too hot & the sealant becomes too fluid, squeezes out of the joint, thins at the edges, & can delaminate from the layer behind it. The window between those two failures for a given laminate & machine is often twenty degrees Celsius or narrower.
Dwell & pressure are not independent of temperature. A line running at high speed gives each jaw less contact time, so the temperature has to rise to compensate, which pushes toward the top of the window & toward the failure mode involving squeeze out. Low pressure gives a seal with channels through it where the two faces met without bonding. High pressure gives a thinner joint & can push product out of the seal area but leaves less sealant in place. The three variables are set together, recorded together, & belong in the batch record together, because a machine setting kept only in the operator's habit is not a specification.
Hot tack is the property most often ignored & the one that causes trouble on viscous products. Hot tack is the strength of the seal while it is still hot & the product is still trying to push it open. A unit filled with a thick product & sealed immediately carries the weight of its own contents against a half-molten joint; if hot tack is poor the seal opens slightly, product sits in the opening, & the final result is a channel leak that passes a visual inspection & fails a dye penetration test three weeks later in a warehouse. Metallocene sealants are chosen specifically for this behaviour, & the drawing of a dwell before the jaws release is often enough to fix it.
Contamination in the seal area is the variable that separates a laboratory sample from a production batch. Anything left on the sealant surface — product splashed during filling, dust from a powder fill, oil from a previous unit — prevents the faces from bonding to each other. Seal-through-contamination performance varies hugely between sealants, & it is one of the few areas where paying for a better grade pays back visibly in reduced leak rates on line rather than merely in a better datasheet.
Fill accuracy in a narrow tube with a viscous product
Delivered accuracy in a single dose unit is rarely discussed because a buyer assumes they are buying whatever the label says. In practice the machine delivers a distribution around a target, the distribution widens with viscosity & with speed, & the target is set above the declared content to keep the whole distribution above the minimum legal fill. That difference is giveaway: product that was bought, filled & shipped but not declared. For a cheap shampoo the number is small; for an active serum in five millilitre stick packs it is a meaningful fraction of unit cost.
Viscosity is the driver. A thin liquid can be dosed by a volumetric piston or a peristaltic head to within a percent or two; a thick cream tails off at the end of the stroke, draws filaments back into the nozzle after the valve closes, & leaves product hanging in the seal area; a product with a yield point, such as a gel with a suspending polymer, does not settle flat before the jaws close & therefore traps air & distorts the unit shape. Each of those behaviours is managed by tooling rather than by tolerance alone: a shut-off nozzle, a suck-back function, a heated head to cut the viscosity locally, & in some cases a piston filler that positively displaces rather than relying on gravity.
Air is the second enemy of accuracy because an entrained bubble occupies volume the product would otherwise fill. It enters during mixing, during transfer, & at the moment of dosing. Vacuum deaeration of the bulk before filling, low shear transfer, & a fill that enters below the surface all reduce it. For a clear or translucent film, bubbles are also visible & become a retail complaint rather than merely a weight problem.
The measurement framework is worth specifying rather than assuming. A checkweigher running at the line speed sampling every unit gives a distribution & a standard deviation; drawing the dosing accuracy & consistency method out is covered in more detail in our note on millilitre output & dose consistency work, & the same logic applies here. What matters for the buyer is the agreement on target weight, declared content, permitted tolerance, & who carries the cost of the giveaway between target & declared.
Stick pack geometry versus the flat sachet
A flat sachet is formed from two sheets sealed on three or four sides; a stick pack is formed from one sheet into a tube, sealed along a longitudinal fin & then across both ends. The difference sounds cosmetic & is mechanical. A stick pack needs accurate web tracking over a longer forming shoulder, a fin seal that must hold without leaking along its whole length, & a cross jaw that has to cut through four film thicknesses rather than two. It therefore runs more slowly per lane for the same seal quality, but it produces a unit that stands up, packs tidily into a carton, pours cleanly, & reads as a newer format to the consumer.
The fin seal is where stick packs fail. A longitudinal seal made slightly off-registration puts less area into the bond; a fin that is not cooled under pressure before it is handled curls & can peel back from the end. The standard checks are a burst or creep-to-failure test on the finished unit & a dye penetration test on a sample drawn from across the run rather than only from the start of it, because a machine drifting slowly out of registration will still be making good units for the first ten minutes.
Opening behaviour is the other half of the choice. A flat sachet is opened by tearing across a notch, which needs a tear notch cut cleanly into only one layer, or by pulling apart two peelable faces, which needs a peelable sealant system set deliberately below its full-strength bond. A stick pack is usually opened by tearing across the width at a notch or a laser score. Tear initiation force, tear direction & the cleanliness of the opening all belong in a specification, because a unit that needs teeth to open is a complaint & one that opens too easily in a handbag is a return. Tear notches also interact with an easy-open requirement & with child resistant expectations in some categories.
Carton & pallet efficiency follow from the geometry. Narrow sticks pack efficiently into a tall narrow carton that merchandises well, but they can be unstable in a case & may need a divider; flat sachets lay down well & ship compactly but look like a sample pile unless presented carefully. Where the product is sold into e-commerce, the outer presentation often decides the inner one, which is the opposite of the order most development briefs use.
Product categories that suit a single dose
Shampoo, conditioner & body wash are the historic core of single dose work: high volume, tolerant of a moderate barrier, cheap enough per millilitre that giveaway does not dominate, & bought in contexts where a small unit is genuinely convenient. Hair masks & conditioning packs need a larger dose, which pushes toward twenty to thirty millilitre stick packs, a heavier laminate, & a higher unit cost. Face masks split sharply: a wash-off clay can go into almost anything, while a leave-on essence behaves like a serum & needs serious barrier thinking. The relative economics of sachet, pot & tube formats for mask products sit at the centre of that decision.
Serums & concentrated actives are the hard case & the one where the format is most often chosen for the wrong reason. A five millilitre unit looks like a cheap way to sample a premium formula, but the surface area to volume ratio is punishing, the product usually contains the most oxygen sensitive & most volatile materials in the range, & the giveaway percentage on a small target weight is high. The answer is usually a foil based structure plus a shorter claim plus a target weight set deliberately close to the declared content, which means accepting a slightly higher rejection rate on the line.
Oils & anhydrous products behave differently from emulsions. Water transmission outwards is not the concern; oxygen inwards & fragrance outwards are, & there is the added problem that a light ester swells polyethylene aggressively. A full compatibility study including the seal integrity after contact & a check for film clouding after several weeks at elevated temperature is not optional for this category.
Powder fills — a single dose of a clay mask, a bath powder, an enzymatic cleanser — invert the whole argument. Dust in the seal area defeats the seal, the product is hygroscopic so water vapour coming in is the dominant failure, & static makes the film cling to the product rather than dropping cleanly. These programmes need an anti-static finish applied to the film, a de-dusting step at the seal before closing, & usually a foil layer. They also need the filling environment controlled for humidity.
Compatibility testing before artwork is committed
A pouch compatibility programme is not complicated & it is routinely skipped because the total elapsed time feels long next to the rest of the schedule. The basic version puts the actual formula into filled units of the actual laminate, holds them at an elevated temperature — commonly 40 °C, sometimes 50 °C for an accelerated read — & holds a control set at ambient & another at a low condition. Units are pulled at intervals & checked for weight change, appearance, seal strength, delamination, odour & the product's own key parameters such as viscosity, pH where relevant, colour & active assay.
The reason it has to happen before artwork is simple: the conclusion may change the structure. If the read at eight weeks shows two percent weight loss & visible seal embrittlement, the fix is a different sealant or the addition of a foil layer, & a different laminate is a different print surface with a different minimum & a different cylinder set. Running the programme in parallel with a structural decision, using the cheapest candidate & the safest candidate simultaneously, is faster than running them in sequence.
Migration & interaction deserve a separate note. The questions to ask are whether anything is moving from the film into the product, whether anything is moving from the product into the film, & whether anything in the product is attacking the structure. Adhesive residues, residual ink components, photoinitiators from ultraviolet drying, slip additives & plasticisers are the usual suspects on the film side; solvents, light esters, high surfactant concentrations, phases at the extremes of pH & certain fragrance materials are the usual suspects on the product side. A headspace check by gas chromatography is an option where odour drift is suspected.
The output of all this should be one document: a compatibility conclusion naming the structure, the fill weight, the seal settings & the recommended storage condition, signed off by whoever owns the specification on both sides. That document is what gets referred to eighteen months later when a reorder behaves differently & nobody remembers which of the two laminates was actually approved.
Line changeovers, print minimums & unit cost
The unit cost of a single dose programme has four components that move independently: film per unit, product per unit including giveaway, machine time per unit, & setup amortised across the run. The first three are roughly linear & easy to quote; the fourth is the one that surprises. A printed laminate minimum typically runs to several thousand metres or a stated number of impressions, whichever the supplier sets; the number of units obtained per metre depends on dose size, so a large dose may exhaust a print minimum in one production run while a small dose may leave most of it in a warehouse.
Machine time is governed partly by the number of lanes. A form-fill-seal machine may have four, eight or twelve lanes, & a twelve lane machine making a small unit is dramatically cheaper per unit than a four lane one. It is also less flexible: registration, filling & sealing across twelve lanes requires the web & the product to behave very consistently, so a difficult formula may end up running on fewer lanes than the machine has. Asking how many lanes a quote assumes is a fast way to understand whether two suppliers are really quoting the same job.
Changeover cost is the other hidden line. Flushing a viscous product out of a dosing system between variants produces waste proportional to the system volume rather than to the run length, so a short run of a difficult product carries a proportionately high loss. Printing makes this worse in a different way: each colour adds a station & a plate or cylinder, each additional SKU on the same web may need its own artwork split, & a change of film supplier mid-programme invalidates the seal window work & the compatibility work in one move.
Finally there is the outer presentation. Single dose units rarely ship loose; they go into a folding carton, a display shipper or a flow wrap multipack. Those have their own minimums, their own artwork lead times & their own structural performance requirements, & they interact with the primary units for stability — a tight carton holding units under pressure can force product toward the seals & turn an adequate seal into a leaking one in transit.
Single dose variables at a glance
The table below sets the principal variables in a pouch or stick pack programme against what each one alters downstream, the compromise that follows, & the point most often missed when the specification is written. The entries are relative directions drawn from ordinary production experience rather than universal values; the figure that matters for a given project has to be confirmed against the actual laminate datasheet & the actual product.
| Variable | What it changes | Typical compromise | Watch point |
|---|---|---|---|
| Laminate structure & foil layer | Water vapour, oxygen & light barrier | Foil gives the best barrier at the highest cost | Flex cracking destroys the barrier locally |
| Inner sealant grade | Seal window & hot tack behaviour | Better grade costs more per metre | Seal through contamination varies by sealant |
| Dose size & surface area ratio | Rate of loss across the film | Smaller doses lose proportionally faster | A five millilitre claim is harder than ten |
| Fill viscosity & dosing method | Delivered accuracy per unit | Thick product widens the spread | Giveaway sits between target & declared |
| Seal temperature, dwell & pressure | Joint strength & channel leaks | Higher speed needs higher temperature | The three belong together in the record |
| Web print minimum & lane count | Unit cost & how long stock is held | More lanes cheaper, less flexible | Print minimum may exceed production need |
| Outer carton & case packing | Retail presentation & transit losses | Tighter packing looks better on shelf | Compression can force product into seals |
Read the rows as a chain rather than a list. The dose dictates the ratio, the ratio dictates the laminate, the laminate dictates the seal window, the seal window dictates the machine speed, & the machine speed dictates the cost per unit. Changing any one of them late means walking back up the chain, which is another way of saying that the cheapest place to make these decisions is at the brief.
What to put in the brief
A workable single dose brief names the format, the dose, the barrier requirement as a derived number rather than an adjective, & the target market climate. Everything else can be negotiated from those four anchors, & without them every supplier fills the gaps differently & the quotes cannot be compared line by line.
- The format: flat four side seal sachet, three side seal sachet, or formed stick pack.
- The dose in millilitres or grams, with the declared content & the permitted tolerance.
- The maximum acceptable weight loss over the claim period, which sets the barrier requirement.
- The climate zones the product ships through & sits in, not only where it is sold.
- The viscosity range & whether the formula contains solvents, high surfactant levels or fragrance.
- The opening method wanted: tear notch, laser score or peelable faces, with the force expected.
- The barrier layers acceptable on cost grounds, including whether aluminium foil is ruled out.
- The retention sample quantity, the storage condition, & who holds the compatibility record.
Then settle the sampling sequence before anything is ordered: formula & laminate candidates tested together, units made on the production machine rather than on a laboratory sealer, seal validation recorded as a setting trio rather than as a description, & a compatibility conclusion signed by both sides. The seal temperature, dwell & pressure that produced the approved units are part of that record, because the same laminate on a different machine will not seal identically.
Where our capability fits
We take a pouch or stick pack programme in that order: barrier requirement derived from the weight loss target first, laminate candidate shortlisted second, seal window characterised on the machine the order will run on third, & artwork committed last. We keep the structure declaration, the seal settings & the compatibility conclusion together in one file per project rather than spread across emails, so a reorder a year later starts from the same three documents instead of from a reconstruction.
We work with brands on private label (your brand on a proven base), OEM/ODM contract manufacturing & full custom formula development, & the dose & laminate are decided alongside the formula rather than after it. The same compatibility & seal validation discipline applies across travel size shampoo in sachet form, a single dose or bottled hair oil programme & a lotion filled into a pump bottle, where the barrier questions differ but the sequencing does not.
Tell us the product, the dose you are considering, the markets & the quantity per SKU, & we will come back with the barrier arithmetic, two laminate options with their print minimums, & the sampling sequence we would run. Start at our inquiry page, email capsulebiotech@163.com, or message us on WhatsApp at +86 158-7655-5319.
General manufacturing information, not regulatory or legal advice. Barrier figures depend on the laminate supplier's test conditions & on the geometry of the unit, minimum fill & declared content rules differ by destination market, & any claim period put on pack has to be supported by stability work on the finished unit in its commercial pack.