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What is UnderCool?

UnderCool is a lightweight garment designed to keep you cool and comfortable in any situation. The unisex design can be worn under virtually anything. Unlike other cooling garments, you can wear UnderCool directly on your skin. With UnderCool you can stay cool and look it too!

How does UnderCool work?

UnderCool uses multiple layers to maximize cooling effect and duration. The garment is made of comfortable wicking fabric to keep you cool and dry and features mesh panels for maximum breathability. The lightweight and flexible phase change material packs are reusable cooling materials for the garment. UnderCool features velcro for easy on and off application and adjustable straps for the best fit.


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Photo of cooling packs made from phase change material.

What is phase change material (PCM)?

Phase change material (PCM) is a category used to describe a wide variety of materials capable of storing and releasing large amounts of energy during the melting/freezing process.

How do PCMs work?

PCMs are substances that absorb and release thermal energy during the process of melting and freezing. In the case of UnderCool, the PCM slowly absorbs your heat over time to keep you cool and comfortable, even in humid environments!

Are PCMs safe?

Not all PCMs are created equal. ThermApparel uses a PCM which is USDA certified bio-based. That means no dangerous oils or hard to clean paraffin waxes.

How long does it take to recharge the cooling packs?

The cooling packs will freeze in any environment under 70˚F / 21˚C. About 20 min in ice water, 40 min in the freezer, 60 min in the fridge 10-12 hours if left on a cold surface in a cold room under 70˚F / 21˚C. We have tested recharging in the snow and it took about 5 min. Please note all recharging times are approximate.


How do you wear UnderCool?

UnderCool is a unisex garment that comes in 5 sizes XS, S, M, L, XL. (Please refer to our sizing guide here for more information.) The garment has adjustable straps and velcro across the front to accommodate the waist of any user. UnderCool can be worn both under and over clothing, according to your preference. We recommend wearing it under your clothes or over a lightweight, breathable fabric for maximum cooling effect. No undershirt required.

How long does UnderCool last?

UnderCool provides you with a comfortable cooling sensation for approximately 2 hours. Cooling times vary depending on external temperatures and activity level.

How much does UnderCool weigh?

UnderCool weighs under 2 pounds.

Will it "sweat" or feel "wet" while I wear UnderCool?

The PCM is sealed in packs within UnderCool. While the PCM does melt as it absorbs heat, the liquid PCM should be kept within the packs. If you experience any wetness from the belt, remove the packs as this could be a leak. The PCM will not harm you but may stain your clothes.

Because of the 70˚F / 21˚C melting temp of the PCM the cooling packs shouldn’t sweat or get you wet like ice and gel packs and won’t burn you skin like ice packs.

Is UnderCool machine washable?

Yes! UnderCool is washer and dryer safe. (Just remove the cooling packs before you wash, trust us on this one. We’ve tried it and they won’t make it. Also, we won’t replace any packs that have been through the washer.)

Can I take UnderCool on a plane?

Possibly. By being prepared with the correct TSA guidelines ahead of time. Read the tips and guidelines we have put together for you.

What are the TSA Guidelines for UnderCool?

The TSA has specific procedures and guidelines when traveling with special needs. We recommend that you review their guidelines to make your trip as easy as possible.

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Photo of woman wearing UnderCool cooling vest while doing yoga.

Can I buy UnderCool?

Yes! You can buy your UnderCool on our shop.

Is UnderCool covered by Insurance?

It depends on your insurance provider and your plan. Most providers cover cooling vests on a case by case basis. You can read more about the application process here.