Pick up almost any fish-oil, vitamin-E, or supplement, and you are likely holding a soft gelatin capsule — a softgel. These sealed, one-piece capsules have become the dominant format for liquid and semi-liquid actives because they are easy to swallow, tamper-evident, and excellent at protecting sensitive oils from oxygen. But the capsule you eat is really a precise formulation, and gelatin is the star of the shell.

This guide explains how softgel shells are formulated, why gelatin remains widely used, and which gelatin properties should be evaluated to support reliable ribbon formation, sealing, drying, and fill release. It also examines how shell composition, fill compatibility, encapsulation settings, and storage conditions can influence seam integrity, leakage, brittleness, sticking, dissolution, and shelf-life performance.

What Is a Soft Gelatin Capsule?

A softel is a one-piece dosage form in which a liquid, suspension, paste, or semisolid fill is enclosed within a plasticized gelatin shell. Unlike a two-piece hard capsule (see our guide to hard capsule gelatin), the gelatin ribbons and fill are brought together during encapsulation and sealed through the rotary-die process. The freshly formed capsules normally undergo primary tumble drying followed by further controlled drying until the specified shell moisture, hardness, seam integrity, and dimensional stability are reached. Softgels can be produced in oval, oblong, round, tube, or customized shapes and can help mask the taste, odour, and appearance of the fill.

The shell is not pure gelatin. It is a carefully balanced film of gelatin, a plasticizer (usually glycerin or sorbitol), and water, with optional colour, opacifier, or enteric agents. The gelatin provides the film-forming backbone; the plasticizer keeps the film flexible rather than brittle.

Getting that balance right is the central skill of softgel development. Too little plasticizer and the shell cracks; too much and it becomes tacky, sticks to the dies, and weeps oil. The gelatin grade sets the ceiling on how robust the film can be, which is why the shell formula and the gelatin specification are designed together, not separately.

Why Gelatin — and What the Shell Requires

Gelatin remains widely used in softgel production because it combines film-forming ability, thermoreversible gelation, mechanical strength, and established rotary-die processability.

• Film formation and flexibility. When correctly plasticized, gelatin can form continuous ribbons with the strength and elasticity required for shaping, filling, and sealing.
• Thermoreversible processing. Gelatin can be prepared as a warm, flowable gel mass and subsequently set as the ribbons cool, supporting continuous rotary-die encapsulation.
• Seam formation. Suitable gelatin rheology, together with controlled ribbon thickness, wedge temperature, die pressure, and machine speed, supports the formation of strong and consistent capsule seams.
• Barrier contribution. A continuous, properly sealed shell can reduce direct exposure of the fill to the external environment. However, oxidation protection also depends on seam integrity, fill composition, headspace, antioxidants, packaging materials, and storage conditions.
• Disintegration and fill release. Standard gelatin shells are designed to disintegrate and release the fill under appropriate test conditions. Any improvement in the bioavailability of a lipophilic active is primarily related to the complete fill formulation and dosage-form design rather than to the gelatin shell alone.

These properties make gelatin suitable for many pharmaceutical and nutraceutical softgels. Performance under high temperature or humidity, or in contact with reactive fill ingredients, must nevertheless be confirmed through appropriate compatibility and stability studies.

For the shell to behave, the pharmaceutical gelatin used must meet tight specifications:

• Gel strength. Gel strength contributes to the mechanical strength and setting behaviour of the gelatin film.
• Viscosity. Viscosity affects gel-mass preparation, ribbon formation, pumping, spreading, and seam development.
• pH. pH can influence processing and compatibility with other shell or fill components.
• Microbiological and chemical quality. Applicable specifications may include microbial limits, elemental impurities or heavy metals, sulphur dioxide, peroxide-related parameters, and other tests required by the relevant pharmacopoeia, customer specification, or destination market.
• Colour and clarity. Raw-material quality, purification, thermal history, and the presence of shell additives influence the appearance of the finished capsule. Particle size can affect gelatin dispersion and gel-mass preparation but does not by itself determine shell clarity.
• Dissolution stability and crosslinking risk. Gelatin source, molecular characteristics, reactive fill ingredients, storage temperature, humidity, and packaging can influence crosslinking and fill-release performance over shelf life. Where the fill presents a known crosslinking risk, a suitable gelatin grade and validated dissolution strategy should be considered.

How Softgel Formulation Works in Practice

A typical softgel shell formula is roughly:

• Gelatin: 30–40 % of the shell mass — the structural base.
• Plasticizer (glycerin/sorbitol): 20–30 % — prevents brittleness and controls texture.
• Water: 30–40 % — drives gelation during casting; most is removed in the drying tunnel.

As a rule of thumb, lowering the gelatin level or raising the plasticizer makes a softer, more elastic shell; raising gelatin or lowering plasticizer makes it firmer and more brittle. The "right" point depends on the fill's oil content, the capsule size, and how the product will be handled and stored. Small pilot runs on the actual fill are the only reliable way to lock the ratio before a commercial run.

The fill itself can be an oil, a suspension of powder in oil, or a paste. The art is matching shell and fill so neither migrates into the other and the capsule stays sealed through drying and shelf life. This is where an experienced gelatin supplier earns its keep — co-developing the grade and plasticizer ratio for your specific active.

How a Softgel Is Actually Made

In rotary-die production, two continuous gelatin ribbons are formed and guided between a matched die pair. The fill is metered through the injection wedge as the dies shape, fill, cut, and seal each capsule. Production output depends on capsule size, tooling, machine model, fill properties, ribbon thickness, seam requirements, and operating speed; it should not be described using one universal output rate.

Freshly formed capsules normally undergo primary tumble drying followed by controlled secondary drying. Drying continues until the validated shell moisture, hardness, seam integrity, and dimensional stability are achieved. Although conventional finished shells commonly retain a relatively low residual water content, the correct drying endpoint must be established for the specific shell formula, fill, capsule geometry, packaging, and stability requirements.

Softgels vs the Alternatives

Frequently Asked Questions

Can softgels be made without gelatin?

Yes — HPMC (plant cellulose) softgels exist for vegetarian positioning, but they seal and barrier differently, so the formulation must be redeveloped rather than swapped. Gelatin remains the default for performance and cost. Gelken can supply both gelatin and HPMC-compatible grades and will advise on the trade-offs for your market, so the choice is technical, not just labelling.

What causes softgel leakage or brittleness?

Usually a mismatch between shell gelatin viscosity/plasticizer level and the fill, or incorrect drying moisture. Tight gelatin specs and a validated drying profile solve most cases. Regular in-process checks of shell moisture during drying catch drift before it becomes scrap, which is why a controlled gelatin viscosity matters as much as the recipe.

Does gelatin affect the active ingredient?

Gelatin is largely inert and dissolves in the stomach, so it rarely interacts with the fill. For acid-sensitive actives, an enteric or Modified Release shell can be engineered on top of the gelatin base. For most nutraceutical oils, standard pharmaceutical gelatin is fully compatible; only a few reactive or highly acidic actives need a special shell.

How long do softgels keep, and how should they be stored?

With a correct shell moisture (typically 5–10 % after drying) and a stable gelatin grade, softgels commonly carry a 2–3 year shelf life. Store them below ~25 °C and away from high humidity to prevent shell softening or sticking, and avoid prolonged sunlight, which can accelerate oxidation of the fill. Gelken can advise on a shell formulation and packaging configuration that meets your target shelf life in the destination market’s climate zone.

Conclusion

Soft gelatin capsules are a triumph of formulation: a precisely engineered gelatin shell that protects, doses, and delivers liquid actives cleanly. Getting them right starts with the gelatin — its Bloom strength, viscosity, and purity set whether your capsule seals, travels, and performs.

If you are developing or scaling a softgel, talk to our application team about pharmaceutical-grade gelatin matched to your fill and die. And for the wider picture, our guides to hard capsule gelatin and gelatin bloom strength round out what every capsule buyer should know. Getting the shell grade right at the design stage is far cheaper than fixing leaks and returns after launch.