Why is gelatin the standard shell material for softgels?

Beyond Biopharma · Pharmaceutical Gelatin FAQ

Short answer: Gelatin is the standard softgel shell because, combined with a plasticiser such as glycerol or sorbitol, it forms a tough, flexible, airtight one-piece shell that can seal around oily or liquid contents and withstand the movement of the fill. Softgels need a film former that is elastic rather than brittle, and a high-viscosity gelatin gives the strong, cohesive ribbon of film the process depends on.

What makes a softgel special

A softgel — or soft gelatin capsule — is a one-piece shell that is formed, filled and sealed in a single continuous operation. Two ribbons of warm gelatin film are fed between rotary dies; the product is injected between them and the dies simultaneously cut and seal each shell. Because the shell is sealed shut, a softgel can hold liquids, suspensions, pastes and semi-solids that a two-piece hard capsule could not easily contain. This is why oily fish oils, fat-soluble vitamins, CoQ10 and many poorly soluble drug solutions are overwhelmingly supplied as softgels.

Why the shell must be strong and elastic

Once sealed, the softgel shell is a permanent bag that has to survive filling pressure, drying, polishing, shipping and years on a shelf — all while bulging and flexing against whatever liquid is inside. That calls for a film that is rubbery, not brittle. Gelatin meets this need naturally: it is cast as a strong gel that stays flexible because the shell retains a deliberate amount of moisture, and the mechanical behaviour of the finished film is tuned by the plasticiser content, the water content and, importantly, the viscosity grade of the gelatin itself.

How gelatin and plasticiser work together

Why high-viscosity gelatin matters

Softgel producers typically reach for a high-viscosity pharmaceutical gelatin. Viscosity is a practical catch-all for the molecular weight and film-forming strength of the gelatin: a higher-viscosity gelatin gives a tougher, more cohesive ribbon that survives the casting and sealing process and yields a denser, stronger shell wall. Because the whole coating idea rests on pulling a uniform, hole-free film, running out of a consistent, strong gelatin means the dies may start producing rejected, poorly sealed capsules. High Bloom grades are used where a firmer shell is wanted, but viscosity tends to be the property that softgel formulators watch most closely.

Protection of air-sensitive and oily fills

Another reason gelatin remains the standard is the physical barrier a softgel gives a liquid fill. The near-watertight, continuous one-piece shell keeps an oil-based contents from leaking, and it offers limited gas exchange so that oxygen-sensitive ingredients inside are protected from the environment to a meaningful degree. That practical airtightness is exactly why volatile aromatic oils and low-oxygen-tolerant actives are so often supplied softgel-ready rather than as powder.

Two further practical advantages deserve mention. Because the shell is delivered and sealed in one shot, no separate capping step is needed and hygiene risk is lower. And because gelatin is animal-derived and easily coloured, softgels are easy to make opaque for light-sensitive fills and to colour-match for branding.

Quality-control language

As with every gelatin application, the numbers that matter — gel strength (Bloom), viscosity, moisture uptake of the plasticised mass, and dissolution or disintegration behaviour of the finished capsule — are best treated as properties to verify against the supplier's certificate of analysis (COA) and the relevant pharmacopoeial test. A specification sheet derived from one fill should always be re-checked when the fill chemistry changes. Read the label on every finished product, and confirm any figure that is not stated on the COA with the supplier or your regulatory body before relying on it.