A blister pack looks like a simple object - a plastic tray with a foil lid - and it is doing more work than most brands realise. The cavity protects the capsule from being crushed, and the lidding decides whether the inside of that cavity stays dry.
That second job is the one that matters for a softgel. Gelatin and plant-based shells respond to humidity: too much and the shell softens, too little and it becomes brittle. The lidding is the barrier standing between the capsule and the ambient air for the whole of the shelf life.
The cavity protects the capsule, the lidding decides how well
Two components, two decisions. The forming film is the material thermoformed into the cavities - it gives the pack its shape, its rigidity and part of its barrier. The lidding is the material sealed over the top, and it provides most of the barrier against moisture and oxygen.
A pack with a good forming film and a poor lidding fails. A pack with a modest forming film and a well-sealed lidding can perform perfectly well. If budget forces a choice, the lidding is where to spend it.
Forming film options
PVC. The cheapest and the most formable. It gives a clear cavity and runs on any blister line. Its barrier is the lowest of the common options, which is acceptable for a short shelf life in a mild climate and not acceptable for a two-year shelf life in a humid one.
PVC with a PVDC coating. The standard upgrade. PVDC is applied as a coating and raises the moisture barrier substantially. Coating weight is specified in grams per square metre, and the barrier scales with it - so "PVDC-coated" is not one specification, it is a range, and the number belongs on your purchase order.
PET. Good clarity, better barrier than plain PVC, and more acceptable in recycling streams than PVC. It forms slightly differently, so cavity design may need adjusting.
PP. Mono-material, which is the reason it is increasingly specified - a PP blister with a PP-compatible lidding can in principle be recycled as one material. Its moisture barrier is good, its oxygen barrier is lower, and it needs the right sealing lacquer on the lidding to seal at all.
Cold-form aluminium. The highest barrier available, essentially impermeable to both moisture and oxygen. It is opaque, slower to run, bulkier per cavity and considerably more expensive. It is the right choice when the fill genuinely cannot tolerate any moisture ingress, and overkill for most.
Lidding: push-through or peelable
Push-through foil. Hard-tempered aluminium with a heat-seal coating. The customer pushes the capsule through it. It is the standard for solid doses and it works well for capsules, provided the push-through force is right.
Peelable lidding. A laminate - often paper, polyester and aluminium - that peels back instead of being pushed through. It is easier for older hands and for anyone with limited grip, and it is the usual choice where accessibility matters. It generally gives a slightly lower barrier than a foil of the same thickness, which is worth checking against your shelf life.
There are also peel-push combinations for child-resistant requirements. If you are selling into a market with child-resistant packaging rules for your product type, raise it at the design stage - it changes both the lidding and the tooling.
Push-through force gets overlooked
Too high and the customer cannot get the capsule out, or crushes it trying. Too low and capsules fall out in transit and arrive loose in the carton. The window is narrower than it sounds, and it is affected by the cavity depth, the capsule size and the foil thickness.
Ask for the push-through force to be measured and stated, and test it with the actual capsule rather than a placeholder. This is a five-minute check that prevents a category of complaint that looks like a product defect and is really a packaging one.
Sealing: three parameters and one compatibility trap
Sealing is controlled by temperature, dwell time and pressure. All three are set on the line and all three are recorded, because a drift in any of them shows up as a weak seal rather than as a visible fault.
The compatibility trap is the sealing lacquer. Lidding is coated with a heat-seal lacquer formulated to seal to a specific forming film. A lidding that seals beautifully to PVC may not seal to PP at all. Changing the forming film without changing the lidding specification is one of the more common ways to produce a pack that looks fine and leaks.
If you are moving to a mono-material PP blister for sustainability reasons, say so early and make sure the lidding is specified to match.
How seal integrity is tested
Three methods are in common use, and they answer slightly different questions.
- Dye ingress. The pack is submerged in a dye solution under vacuum, then opened and inspected for dye that has entered a cavity. Good at finding channel leaks - the tiny unsealed paths along a seal that visual inspection misses.
- Vacuum decay. The pack is placed in a chamber, a vacuum is drawn, and the pressure is monitored. A leaking pack loses vacuum. Non-destructive, which means the same units can go on to stability.
- Visual inspection. Cheap, fast, and only catches the obvious. Useful as a line check, not sufficient on its own.
Ask which method is used and how many units per batch. For a capsule product, dye ingress or vacuum decay on a stated sample size is the reasonable ask, and either is far cheaper than a recall.
Cavity design and count
The cavity has to fit the capsule, not just contain it. A capsule that rattles in its cavity will scuff and may break; a cavity that is too tight makes push-through difficult and can deform the capsule. Depth, draft angle and corner radii are all set against the specific capsule dimensions.
Novelty shapes need bespoke cavities. A heart or a mushroom capsule in an oval cavity either will not seat or will not present well, and a bespoke cavity means a bespoke forming tool - a second tooling item that belongs in the budget.
Count and layout drive the carton size and the retail format. Six cavities in a single row suit a trial pack. Thirty in a grid suit a monthly pack. If the product is going on a peg, the pack needs a hanging slot and the layout has to leave room for it. Perforations between cavities let a customer tear off a single dose for travel, which is a genuinely liked feature and costs almost nothing.
Material and lidding at a glance
| Option | Moisture barrier | Recyclability | Cost | Fits |
|---|---|---|---|---|
| PVC | Low | Poor | Lowest | Short shelf life, mild climates |
| PVC / PVDC coated | Moderate to high, by coating weight | Poor | Low | The default for most capsule packs |
| PET | Moderate | Better | Moderate | Where PVC is unwanted |
| PP with matched lidding | Good | Best - mono-material | Moderate | Recyclability-led briefs |
| Cold-form aluminium | Highest | Recyclable where collected | Highest | Moisture-critical fills |
Humidity is the failure mode
Softgel shells are hygroscopic. Their water content equilibrates with the surrounding air, which is why production areas are humidity-controlled and why the pack barrier matters so much.
A capsule stored at high humidity softens and can stick to the cavity or deform. At very low humidity it loses water, becomes brittle, and can crack on push-through. Both failures look like a manufacturing defect to the customer and both are prevented by specifying the right barrier for the climate you are actually selling into - not for the climate the factory sits in.
Tell your manufacturer where the product will be sold. A pack designed for a temperate European market can fail in Southeast Asia. Our humidity control article covers the production side, and our seam integrity article covers how shell problems present.
What to test before approving a blister
- Seal integrity by dye ingress or vacuum decay, on a stated sample size, from production tooling.
- Push-through force, measured with the actual capsule.
- Stability on the finished packed blister, including the humidity conditions of your target market.
- Transit testing on the packed carton - blisters protect capsules well, but cartons still get crushed.
Stability on the finished pack is the one that matters most, because it tests the film, the lidding, the seal and the capsule as one system. Testing the capsule in bulk and assuming the pack performs is a common and avoidable gap. Our stability testing guide sets out the protocol.
How to brief a blister pack
Give the capsule dimensions and shape. Give the count and whether the pack is a trial, travel, monthly or gift format. Give the markets and, if you know them, the storage conditions the product will see - a humid market is a different specification from a dry one. Give the shelf life you need, because that is what sets the barrier. Say whether recyclability is a purchase driver, since that pushes towards mono-material. And say whether the pack goes on a peg or into a carton.
Ask for the forming film specification and the lidding specification in writing, including the coating weight if PVDC is used. "Blister pack" on a quotation is not a specification.
Where our blister capability fits
We pack capsule serums into blisters across the material range, including a 6-piece argan blister pack built as a trial and travel format. Cavity design is done against the actual capsule, including bespoke cavities for shaped capsules such as our heart-shaped capsules.
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.
Tell us the count, the market and the shelf life you need, and we will come back with a material and lidding specification with the barrier numbers stated. 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.
General manufacturing information, not regulatory or legal advice. Claim limits vary by market.