Powder-in-oil capsules look simple on a shelf: a translucent shell, a golden fill, plus a fine cloud of particles suspended inside. Brands ask for them because the visual is distinctive plus the dose is sealed. The manufacturing reality is less forgiving. A powder phase that stays evenly dispersed in a bulk tank can settle inside a capsule within hours of filling.
This is a formulation question before it is a marketing one. Particle size, oil viscosity, fill temperature, plus the way the mass behaves at the nozzle decide whether the idea survives scale-up. The capsule format also removes the hardest part of suspension design: keeping the product uniform in the hands of the customer.
A sealed dose solves the settling problemA bottle of suspended serum asks the user to shake it, plus to accept that the last dose looks different from the first. A softgel asks for nothing. Each unit is filled once, sealed once, plus delivered in the same state it left the line. There is no headspace to separate, plus no dependence on the customer to redisperse the product.
Sealing also settles the oxygen question. An opaque shell blocks light plus limits oxygen ingress, which is why most sensitive powder phases travel better in a pigmented or pearl shell. A clear shell shows the suspension beautifully but exposes the fill, so the choice between shelf appeal plus protection should be made early.
What actually holds the particles in placeVery few capsule fills are true suspensions. Most are oil-continuous systems thickened enough to carry the powder without making the fill unpumpable. The useful levers are:
- Silica plus clay thickeners that build yield value without adding colour
- Coated or encapsulated powders that resist oil migration over time
- Mica or mineral pigments used at low loadings for pearl effect
- Fine botanical powders, which need tighter sieve control than synthetic grades
Powder loading is the number that governs everything else. Below roughly ten percent, most oils stay workable. Above it, viscosity climbs, fill flow becomes uneven, plus seam strength on the shell starts to suffer. A beaker sample will not predict any of this, because it has no nozzle, no dwell time, plus no cooling curve.
Where suspensions fail at scaleSettling is slow in a capsule but not absent. Particles drop at a rate set by size, by the density gap between powder plus oil, plus by the viscosity of the continuous phase. Halving particle size cuts that rate sharply, which is why fine grades are worth the cost. Two other failure points matter as much. Air entrained during homogenisation shows up as a foamy band in the filled capsule, plus bulk mass held too long in the hopper drifts out of specification before the run ends.
Four numbers to agree before the first batch- Target particle size plus the sieve cut that will be accepted
- Powder loading as a percentage, with a tolerance band
- Fill mass at production temperature, not at room temperature
- Shell material plus opacity, whether gelatin or a plant-based shell
CapsulesBiotech runs this work across facial oil, eye serum, hair oil, body lotion, face cream, plus mask formats, in softgel sizes from 0.2ml to 1ml. Both shell types are available, food-grade gelatin plus a fully plant-based option, so the suspension can be matched to the climate it ships into plus the claim the brand wants to make. Send us your target market, your positioning, plus the dose you have in mind. We will come back with a formula direction, a fill specification, plus a realistic run plan.