The cooling hit is the single most quoted reason people prefer hydrogel over a cloth sheet mask. It is not menthol and it is not because the mask was in the fridge. It is thermal conductivity, and it can be engineered.
Sample imageThree separate mechanisms, not one
What a user calls "cold" is actually three effects stacked, arriving in a sequence.
1 · Conduction — the big one
A hydrogel sheet is 60–90% water. Water conducts heat roughly twenty times better than still air (about 0.6 vs 0.026 W/m·K). A cloth sheet mask is mostly air trapped in fibre; a hydrogel sheet is essentially a slab of water held in a gel.
So when the gel touches skin at, say, 22 °C room temperature against 33 °C skin, it pulls heat away far faster than any fabric can. That is the initial hit, and it is immediate.
2 · Thermal mass — how long it lasts
Water also has an unusually high heat capacity. The mask does not just conduct heat away, it stores a lot of it before its own temperature rises to match the skin. A thicker, wetter sheet holds the cooling longer; a thin one equilibrates fast.
This is why cooling duration is a thickness decision, not a fragrance decision.
3 · Evaporation — the tail
At the exposed edges and any uncovered surface, water evaporates, and evaporation removes heat. This is a smaller contribution on an occlusive gel sheet than people assume — the gel is largely sealing the skin, not letting it breathe — but it becomes the dominant effect as the mask thins out toward the end of wear.
Strong hit on contact, a plateau while the sheet equalises with skin temperature, then a slow decline. The perceived cooling does not last the whole wear time on any hydrogel mask, and a brand that promises it will is setting up a disappointed review.
What menthol actually does — and why it is a different thing
Menthol, and cooling agents in the same family, do not lower skin temperature. They bind to the TRPM8 receptor, which is the receptor that reports cold. The nerve says cold; the thermometer does not agree.
That is a legitimate formulation tool, and it has two properties worth knowing:
- It persists long after the thermal effect has faded — useful if you want cooling to last the full wear time
- It stings on compromised or eye-adjacent skin, and it is a common cause of complaints on eye patches specifically
Our general position: use the physics for the initial impact, and reach for a cooling agent only if the brief genuinely needs sensation past the thermal plateau — and then at a restrained level, and not on an eye patch without testing.
The four levers you can actually pull
| Lever | Raises cooling by | What it costs you |
|---|---|---|
| Higher water content | More conduction, more thermal mass | Lower gel strength, more tearing, more syneresis |
| Greater thickness | More stored cold, longer plateau | Heavier sheet, more slippage, higher material cost |
| More free essence in the pouch | Extra cool liquid at the moment of application | Slippage; a wet, dripping first impression |
| Cooling agent | Sensation that outlasts the physics | Sting risk, especially near the eye; not a real temperature drop |
"Refrigerate before use" on the carton is the cheapest cooling upgrade available to a brand. It costs nothing, it works, and it converts the product into a small ritual. It also, in our experience, produces some of the most enthusiastic reviews a mask gets — and it needs no reformulation.
What to specify if cooling is the point
- Water content — state a target and a range, not just "high"
- Finished thickness — the main lever on duration
- Free essence charge per pouch — and how it is measured
- Cooling agent — whether you want one at all, and if so an explicit eye-area sting test
- How you will test it — a simple skin-surface thermometer reading at 0, 2, 5, 10 and 20 minutes is enough to compare two candidate formulations, and it is far more useful than a panel saying "it feels nice"
Developing a hydrogel product?
Yanse manufactures hydrogel eye patches, face masks and lip masks at our own ISO 22716 plant in Fujian — 8,000 m², Class-100,000 cleanroom, 11 QC checkpoints, audited on-site by L'Oréal, Watsons, MINISO and Mentholatum. Our hydrogel line is a three-head system, so two or three formulations can be laid down side by side in a single sheet. Plant-based gel system: halal and vegan compatible as standard.
Request samples & specifications →Three-zone capability · plant-based gel · halal & vegan compatible · 24-hour reply · NNN before any formulation work
Educational content for brand and product teams. Ingredient and claim information is general and varies by market regulation; finished-product claims should be confirmed against the rules of your target market. Yanse Cosmetics is a contract manufacturer (OEM/ODM) and does not sell finished consumer goods under its own brand. Trademarks referenced belong to their respective owners; no comparison or equivalence claim is made.