better health through cooling
designed for multiple sclerosis, lupus,
diabetes, and dysautonomia

A man and woman wearing UnderCool 3 lightweight concealable PCM Cooling Vest

UnderCool 3

most concealable

Folded RallyWrap Cooling Wrap with PCM Cooling Pack coming out of one pocket


easy on/off

UltraCool CoolingVest showing 8 included PCM Cooling Packs


max cooling


Free Shipping
Easy Exchanges/Returns


60 day exchange/return


Made in the USA


Awesome Customer Service Yes, we really do answer

Don't let heat dictate your day.

stay cool, comfortable, and in control, empowering you to live life to the fullest by helping to...

  • reduce fatigue
  • beat cog fog
  • enable exercise
  • explore the world
Woman hiking with friends up a mountain in a UnderCool 3 PCM Cooling Vest concealed underneath her shirt.

“I have always wanted to climb a 14er and wanted it to be Mt. Sneffels. I have had issues with heat and being very fatigued on regular hikes. But with the ThermApparel Cooling Vest I was able to hike ten miles and summit my 14er. I changed my packs at the top, a total of 8 hours they kept me cool enough to achieve my dream while living with MS. Thank you!”

~ Amee Waldvogle, Colorado

Amee’s Cooling Product of Choice
1 Medium White Vest Garment
2 Sets of ExtendedCool Cooling Packs

Man standing in from of his miata racecar while wearing a UnderCool 3 PCM Cooling Vest under his firesuit.

“Lowered my core temp by a FULL 3 degrees.”

~Charlie Bohley, New York

Female Runner standing on a street wearing an UnderCool 3 PCM Cooling Vest before a 5k road race

“I use mine for everything from taking the dogs out to performing on stage to running a 5k.”

~Tiffany Tallent, Tennessee

Woman in bicycling gear and UnderCool 3 PCM Cooling Vest under her biking attire during her BikeMS event.

“I do not have to stay at home sheltering in place. I can care for my grandbaby, run errands and, bike! Bicycling is my preferred exercise because of my MS gait & balance problems that make walking very tiring. I love this product. It's paidfor itself already in the safety and security I feel when I take it with me during hot weather.”

~Margo Elwood , Oregon

Man playing Wheelchair Baseball while wearing UnderCool 3 PCM Cooling Vest underneath KC Royals Jersey

I can not sweat due to my C7/T1 spinal injury and it affects my sports performance. Using the Cooling Vest in wheelchair Rugby kept my post-game temps safe at 98-99°F, enhancing my focus without constant cooling.

~Tom, Kansas City

Woman with Multiple Sclerosis standing in front of Petra wearing UnderCool 3 PCM Cooling Vest

It enables me to do the things I want to do, w/o people knowing that I have it on. I traveled to the Jordan deserts, and had great relief from 100F temps.

~AnnaMarie Prono, New York

Female Gardener pulling carrots from garden, wearing UnderCool 3 PCM Cooling Vest under her overalls

“I use it when I garden and also at the gym. I'm a fitness instructor and it makes it easier to teach. It has made it so that I can do hard things longer.”

~Ruth, New York

Older Woman Tennis player holding her racket and wearing UnderCool 3 PCM Cooling Vest concealed under her clothes

“I use it when I play tennis. Couldn't do without it in the heat.”

~Linda Lane, Ohio

Santa Jim giving a wink to the viewer, wearing UnderCool 3 PCM Cooling Vest concealed under Santa Suit.

“I never have to worry about overheating again. It’s invisible under my vest and Santa Coat. It keeps me cool during home visits sitting near the fireplace or in the hot sun at the Christmas in July events. My ThermApparel Cooling Vest will always be part of my Santa Outfit, summer and winter.

~Santa Jim, New York

Female horseback rider on her horse wearing UnderCool 3 PCM Cooling Vest concealed under her shirt

“Thanks to my ThermApparel Cooling vest, I am able to battle the hot summer days with my boy, doing what I love, rein, cow horse and cutting!!!”

~ Tanya, Canada

Female Kayaker on Lake Ontario wearing a UnderCool 3 PCM Cooling Vest under her Personal Flotation Device

“Kayaking in the sun can be hot, so I wore my Cooling Vest. It really helped out and after 2 hours when the sun was fading, I realized they were making me almost too cool, so I had to take them off!”

~ Allison, New York

A furry wearing a custom built costume with a concealed UltraCool PCM Cooling vest underneath

The vest was awesome, ten minutes into a regular fursuit photoshoot I'd be sweating, but we took photos for 2 hours and I didnt break a sweat. It’s also really lightweight and comfy and at one point I forgot I had it on"

~Salmon, New York

A woman living with MS hiking with 2 hiking poles and her UnderCool 3 PCM Cooling Vest.

This summer I had my first real chance to put my ThermApparel Cooling Vests to the test. My husband and I drove from Phoenix to Denver and spent several days in the National Parks in Utah. I was really nervous about hiking in the warm weather in Utah in late June, but thanks to my cooling vest, I was able to hike in all five parks that we visited. It is such an awesome piece of equipment! I love, love, love the freedom it gives me during the hot weather.

~Kim Klein, Arizona

Kim’s Cooling Choice
2 Large Black Vest Garments
2 Sets of ExtendedCool Cooling Packs


Stay cool anywhere.

Works great in humid and dry climates


Cooling that lasts.

Cooling packs last 1-4 hours depending on product.


Stay energized.

Lightweight cooling power that won’t drag you down


Feel great.

4-way stretch comfortably fits all bodies and moves freely with you


Stay in the game.

Ultrafast recharge times and 1000 reuse’s mean you’ll always have cooling

Easy to use

Easy to use

Cool It

place in the fridge, freezer or ice water

Wear It

insert cooling packs into the pockets

And Go...

anywhere you want, doing anything you want

Cool It Wear it And Go

Don’t just take our word for it...

ThermApparel believes in leveraging creativity, empathy, and dignity of the human spirit to help others break barriers related to heat sensitivity. We strive to provide independence and a more active lifestyle to people living with heat sensitivity from conditions like Multiple Sclerosis, Lupus, Dysautonomia, and POTS. In fact, we designed our the UnderCool just for them!

Do you know what is just as bad as heat stress? Financial Stress. So we have teamed up with leading non-profit organizations to help you out when you need it. Check out the list here.


Experience the magic of PCM cooling

Meticulously designed PCM cooling packs provide continuous cooling comfort by absorbing body heat and complementing your body’s natural cooling process, effectively lowering your core body temperature.

ThermApparel PCM cooling packs fit discreetly into our products pockets, providing hassle-free cooling without the need for soaking or plumping.

Where cooling meets comfort.

Where cooling meets comfort.

4-Way Stretch Fabric adapts to your body's contours and movements for a tailored fit and ultimate flexibility.

Perfect for yoga, running, climbing, or keeping up with the kids, it retains its shape and elasticity over time, ensuring lasting comfort and performance.

Want to take a deep dive into our tech? Check out our How it Works section.


Why we’re better


pcm cooling system

  • icon works in any climate
  • icon cools your core body temp
  • icon lightweight and flexible
  • icon dry conformal cooling


evaporative cooling

  • icon doesn't work in humidity
  • icon cools your skin, NOT your core directly
  • icon lightweight and flexible
  • icon must be wet


gel & ice cooling

  • icon work in any climate
  • icon too cold for direct skin contact
  • icon heavy and rigid
  • icon wet from condensation


Maximum cooling that wraps all the way around your body in a form factor that mimics the UnderCool.


Versatile cooling power to use as a belt, seat cushion, or sash. Great for Pre- and Post- Cooling.


UnderCool 3

The cooling vest that started it all. Concealable, lightweigh and comfortable coolling for everyday needs.


To find your perfect fit, simply measure your natural waist—right where you bend naturally. Picture the 'I am a little teapot' song: where you 'tip me over and pour me out'—that's the spot! Need more guidance? Head over to our sizing page, complete with an instructional video!"

Stay cool with our 60-day guarantee: either love it or get your money back! And hey, if you need a swap, we've got you covered—for free! Give us a shout at 1-855-232-7233 from 8:30 am to 4:30 pm EST. It's all about keeping things cool and hassle-free!

Our cooling packs are the champions of convenience! They recharge in record time: just 20 minutes in ice water, 40 minutes in the freezer, or 60 minutes in the fridge. No extra steps needed from you! Want to geek out on the details? Dive into our tech page for more!

Absolutely! Give us a shout at 1-855-232-7233 from 8:30 am to 4:30 pm EST, and watch in amazement as a real human picks up the phone! Prefer to keep it digital? Jump into our live chat for lightning-fast assistance!

Let our happy customers do the talking! Dive into our testimonials and see why they're raving about us!


New York

"It's been a total game changer in terms of being able to do outdoor events. It helps me keep my core temp down. I’ve worn it kayaking and to run errands because I get really warm and it's amazing."


Bethany Hill

"Bravo to ThermApparel! I don't think I could have done my yard work, which involves trimming off 8' high sections from my bird of paradise trees without my vest. My Cooling Vest outlasted me and my undeniably strenuous activity as well as the "feels like" 88 degree weather with sunshine.”


Ben Mandrell

"I wear my UnderCool when I work out, It helps me stay in the game. I can run a lot better and get more out of my workouts. It has allowed me to get back part of the life I lost when I had the MS diagnosis. It has definitely allowed me to enjoy my life."



"I have been so stubborn about not wanting a cooling vest, but I should have bought one sooner. They have been life changing. When I'm wearing one, I'm able to participate in activities without debilitating fatigue. Thank you for helping me to feel a little bit more normal again.”


New York

"My body can't take the heat; walking becomes impossible and who wants to say indoors. Summer time means fun in the sun. Thanks to the UnderCool Cooling Vest I am able to be out and about. I have almost every type of cooling vest out there and none of them are as discreet nor stay as cool as the Thermapparel Cooling Vest.I wear the vest and I can handle a simple workout routine."


Santa Ed Taylor

"This vest adds almost nothing to the cookie zone.”


Christine Paternostro
New Jersey

"NOW I CAN enjoy all that Walt Disney World has to offer without worrying about walking or the weather! I am BEYOND happy. It let me enjoy my favorite place with my favorite people and my heat-related MS symptoms were kept at bay.”


Terry Justack

"My UnderCool vest has allowed me to golf in warmer weather that would normally be too hot for me to play due to my MS.”

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.