The shell of a serum capsule is usually treated as packaging. It is not. The shell exchanges moisture with the fill, sets the storage window, decides whether your product can be sold as vegan or halal, and determines how the capsule behaves in a hot warehouse. Choosing it is a formulation decision that happens to have marketing consequences.
This article compares gelatin and plant-based softgel shells on the criteria that actually affect a launch: cost, fill compatibility, humidity behaviour, certification status, and what each choice means for your labelling.
The shell is not a container, it is part of the formulation
A softgel shell and its fill reach a moisture equilibrium. Water moves from whichever side has more of it to whichever side has less, until the two balance. That means the shell is continuously interacting with your formula, not merely holding it.
The practical consequence: a fill that is stable in a glass bottle may destabilise a capsule shell, and a shell that performs well in a temperate climate may fail in a hot, humid one. This is why shell selection belongs in the formulation stage rather than the packaging stage.
What gelatin shells are made of
A conventional softgel shell is a gel mass of gelatin, water, and a plasticiser - most often glycerol, sometimes sorbitol or a blend. Gelatin is a protein obtained by partial hydrolysis of collagen, and its sources are typically bovine or porcine, though fish gelatin exists for specific requirements.
Gelatin is used because it behaves predictably. It forms a strong, elastic film, seals reliably under heat and pressure, and tolerates a wide range of fill viscosities. It is also the cheapest option at scale and the one with the widest equipment compatibility. Most existing softgel lines are set up around gelatin rheology.
The limitations are real. Gelatin is animal-derived, which rules out vegan positioning and complicates halal and kosher claims unless the source and the processing are documented. Gelatin shells are also sensitive to high humidity and to temperatures that approach their melt point, which matters for shipping into hot climates.
What plant-based shells are made of
Plant-based softgel shells replace gelatin with a film-former derived from seaweed, starch, or fermentation. The common options differ meaningfully in behaviour:
- Carrageenan-based systems use a seaweed polysaccharide, usually with a starch and a plasticiser. They run on adapted equipment and are the most established plant-based option for softgels.
- Starch-based systems use modified starch, often blended. They tend to produce a more opaque shell and can be more brittle at low humidity.
- Pullulan is a fermentation-derived polysaccharide. It produces a clear, glossy shell with good oxygen barrier properties. It is more expensive and less commonly used for large cosmetic runs.
- HPMC (hydroxypropyl methylcellulose) is well established for hard two-piece capsules and is used in some softgel systems, though it behaves differently from gelatin on the die.
None of these is a drop-in substitute. Each has its own gel mass temperature window, its own setting behaviour, and its own sensitivity to fill composition. A line validated for gelatin usually needs process adjustment to run a plant-based mass.
Cost and lead time differences
| Factor | Gelatin shell | Plant-based shell |
|---|---|---|
| Raw material cost | Lowest of the common options | Materially higher, varies by system |
| Equipment fit | Standard on most lines | May need process adjustment |
| Development time | Shortest, best-understood behaviour | Longer; trials often needed |
| Yield / reject rate | Generally the most forgiving | Depends on system and operator experience |
| Vegan positioning | Not possible | Possible, subject to full check of inputs |
| Halal / kosher | Possible with documented source | Often simpler, still needs documentation |
The cost gap is not only the raw material. Development time is longer for a plant-based shell the first time a factory runs it, and reject rates during the first commercial batches are usually higher. Both should be priced into your first run rather than discovered afterwards.
Fill compatibility: which fills suit which shell
Fill compatibility is the most under-discussed part of this decision. Some fills that run beautifully in gelatin cause problems in a plant-based shell, usually around seal strength or around moisture movement.
Factors that commonly cause trouble include high levels of certain polyols, surfactant-containing fills, and fills with a significant polar fraction. Oil-based fills built on esters or squalane are generally the easiest to accommodate across shell types.
The honest answer is that compatibility has to be tested with your actual fill. A supplier who tells you any fill runs in any shell without a trial is guessing. Ask for a pilot run with your formula, not a generic compatibility statement.
Humidity and temperature behaviour
Gelatin shells soften as humidity rises and can deform or stick at temperatures that a warehouse in a hot climate will reach. Plant-based shells have their own sensitivities: some starch-based systems become brittle when the air is very dry, and certain carrageenan systems are sensitive to prolonged high humidity.
This is a shipping question as much as a formulation one. If your distribution includes a humid market or a non-climate-controlled last mile, say so during development. The shell, the secondary packaging and the storage instructions should be decided together. Moisture behaviour in production is covered in our article on water activity and humidity control.
Halal, kosher, vegan and market requirements
Certification is a documentation exercise, and it starts with the source of every input. For gelatin, the animal species and the processing method both matter, and halal and kosher authorities differ in what they accept. For plant-based shells, vegan status is easier but not automatic: some systems use processing aids or plasticisers that need checking.
If certification matters to your market, request the certificate chain before you place the order, not after. Certificates have expiry dates and scope limits, and a certificate that covers one product does not automatically cover yours. Market-specific labelling rules are summarised in our labelling guide by market.
Shelf life and hardening
Both shell types harden over time as moisture equilibrates and, in some systems, as cross-linking progresses. Hardening changes the user experience: a capsule that was soft and pleasant at month two may be noticeably firmer at month eighteen, and in worst cases the shell becomes slow to break when the user twists it.
This is why shell selection should be made together with a stability programme. Accelerated and real-time data on a specific shell and fill combination is the only reliable predictor. Our stability testing guide sets out what to commission.
How the choice affects your claims and labelling
The shell appears on your ingredient list, and in some markets the source matters to consumers reading the pack. A vegan claim is only defensible if every input, including processing aids, is verified. A halal claim needs a certificate whose scope covers the finished product.
There is also an interaction with the rest of your range. If your brand positions itself as vegan, a gelatin capsule is a visible inconsistency even when the serum itself is plant-based. Consistency across the range is usually worth more than the cost saving on the shell.
What to ask your manufacturer
- Which shell systems have you actually run at commercial scale, and for which fills?
- Will my fill need a pilot trial, and is that included in development cost?
- What is the target shell moisture at release, and how is it measured?
- Can you provide the certification chain for the shell and the plasticiser?
- What storage and shipping conditions does this shell require, in writing?
The quality of the answers tells you more than the price. A manufacturer who has run plant-based shells commercially will answer these without hesitation.
Where our capsule capability fits
We run gelatin softgel shells for standard capsule serums including custom softgel face serum capsules and vitamin E softgels, and we support plant-based shells where the brief and the fill allow it. Both routes start with a fill trial, because that is the only way to know whether a shell will hold your formula.
We work with brands on private label (your brand on a proven base), OEM/ODM contract manufacturing, and full custom formula development - whichever matches where your brand is today.
Send us your target market, your positioning requirements and the active you want inside, and we will tell you which shell will actually hold it. Start at our inquiry page, email capsulebiotech@163.com, or message the right team on WhatsApp: Capsule Series (capsules only) +86 158-7655-5319, Cosmetics Series (serum, hair care, body care, fragrance) +86 158-7655-5319.
This article is general manufacturing information, not regulatory or legal advice. Certification and labelling requirements vary by market and certifying body.