Best Savings of the Year!

$50 off Bundles 

do more
of what you love


“lowered my core temperature
by a full 3 degrees”

ThermApparel Adventure Bundle
Med. Black/White, ExtendedCool Packs


benefits of UnderCool

  • Improve performance
  • Reduce fatigue
  • Keep your focus
  • Faster recovery

UnderCool works by absorbing heat away from your body in a lightweight, long lasting, and comfortable cooling vest.

how does it do that?

Unique Garment Design

UnderCool vest uses 4 way stretch for a snug fit and strategically placed cooling packs for comfort and concealability.


Advanced Cooling Technology

ThermApparel Cooling Packs take into account human physiology, freezing at the perfect temperature to cool your core body temperature and work with your bodies natural cooling system.

more ways to use


Wear 30-60 min prior to activity and start with a cooler core for more peak performance.


Wear under your favorite outer layer of clothing to reduce your heart rate and heat strain.


Slip on easily after your workout to cool down quickly and reduce stress on your body.


Trust in Us! 60 days to try.

If a vest remains in your closet because you are too embarrassed to wear it, well, then it is of zero help. Invest in your health and happiness with a durable, comfortable cooling vest. To prove it ThermApparel has a 60 day exchange/return policy for a full refund less shipping provided the vest is returned in like-new condition.

Womens and Mens Sizing

Use your preferred shop to get the best measurements for your perfect fit. The products are the same in each shop. To get the maximum cooling effect from a vest, it should fit snugly around your body.

stay strong. no compromises needed




1 - 3 hours cooling time

SlimCool Packs 1-2 hours cooling time.
ExtendedCool Packs 2-3 hours cooling time.


slim fitting, easily transportable

7 sizes and 2 colors. Adjusts to fit a wide variety of body shapes and sizes. No zippers or snaps.


machine washable

Mild detergent, cold water, air dry


safe effective cooling temperature

Cooling Packs freeze at 70F/21C. Not too cold or too hot. Keeping you comfortable and works with your bodies natural cooling.


lightweight, comfortable, reusable

SlimCool Packs Weight - 1.3 lbs.
ExtendedCool Packs Weight - 1.9 lbs.


4 Way Stretch Fabrics

Provides comfort and optimal cooling


Did you know?

UnderCool cooling packs freeze at 70F working with your body to improve cooling. Other products which use Ice or colder PCMS for cooling can cause blood vessels to constrict. This prevents the cooling from reaching other parts of our body, and can cause your core to actually heat up by preventing the flow of blood to your extremeties.

“I didn’t overheat at all and I still felt good”


76 weeks with a 100+ mile bike ride

ThermApparel UnderCool
XS Black, ExtendedCool Packs

Why cooling is important?

Our bodies are always producing heat. Its up to our hearts and blood vessels to get that heat away from our core organs. Using a cooling vest makes life easier on your heart to keep you safe and give you more energy for what you care about.

4 ways to refreeze and store.

Did you know UnderCool cooling packs freeze at 70°F / 21˚°C.
Allowing for lots of ways to refreeze and store.

Refreeze quickly in a cooler with ice water for a cool 32°F / 0°C

Cooling packs will refreeze in ice water in 15-20 min.


Store in the freezer for a brisk 0°F / -17°C

Cooling Packs refreeze in 45 min. Safe to store in freezer for long term, if not wearing right away, taking to an event or need the extra few minutes of cooling.


Store in the fridge for a cool 40°F / 4°C

Cooling Packs refreeze in 60 min. Safe to store in fridge for long term. Cooling Packs will be at a comfortable temperature to put on right away.


Store in A/C for a mild 68°F / 20°C

Cooling Packs refreeze in 8-12 hours. They may not feel cold to the touch but they are working to keep your core cool.



“I used to dread playing tennis in the heat, but now I don’t give it a second thought”


ThermApparel Adventure Bundle
Small White, ExtendedCool Packs


frequently asked questions

1. How long will an UnderCool keep me cool ?

Cooling packs will stay cold for 1-3 hours depending on your level of activity and the ambient temperature. ExtendedCool Cooling Packs last 2-3 hours. SlimCool Cooling Packs last 1-2 hours. To learn more about the cooling packs check out our tech page.

2. Many Cooling Vests seem too heavy for sports, how is UnderCool different?

The UnderCool is significantly lighter than most cooling vests weighing at most 2 lbs. As we all have experienced where the weight is carried also has a dramatic impact on how it affects us. Because the UnderCool uses 4 way stretch fabrics and the cooling packs are situated against your lower back you will not feel the weight at all.

3. How do I find my correct size?

Currently UnderCool comes in 7 sizes XXS - XXL to fit a wide variety of body shapes and sizes, because "one size fits all" really isn't true. UnderCool should fit your body like a glove to give you the best cooling support.

Sizing is dependent on your natural waist measurement, not your bust, shirt or pant size. You will most likely wear a vest smaller than what you think. Not sure where your natural waist is or how to get the correct sizing? Check our sizing guide to get the correct UnderCool for you.

4. How do I recharge the Cooling Packs?

Our Cooling packs are the easiest and fastest to recharge for their next use. The packs can refreeze in ice water in 20 min, in the freezer in 40 min, and in the fridge in 60 min. Nothing else from you is required. To learn more about the cooling packs check out our tech page.

5. What if the UnderCool doesn't work for me? Can I return or exchange it?

Yes. We have a 60 day return/exchange policy.


four things to decide before you buy

Bundle your order and save.

Upgrade from an UnderCool to a Festival or Adventure to save on extra sets of Cooling Packs or an extra Vest Garment.


White or black, pick your color

If you wear more dark clothing order black. If you wear more light clothing order white. If you still can't decide, buy an Adventure and get both colors!


Correct fit = best cooling

A snug fit ensures optimal cooling. With 7 sizes XXS - XXL, you will find you perfect size.


Cooling time vs. weight

ThermApparel offers 2 cooling pack options.
ExtendedCool lasts 2-3 hours and weighs 1.9 lbs.
SlimCool lasts 1-2 hours and weighs 1.3 lbs.


Questions about our vests or shipping? Reach out to the ThermApparel team toll-free at 855-232-7233, write to us through our website’s contact form or chat with us via live chat. We always respond because, otherwise, that wouldn't be cool.