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 needs to fit your body like a glove to give you the best cooling support. Watch Julia explain how to get the best measurement and figure out the right size. 


Sizing is dependent on your natural waist measurement, not your bust, chest size or pant size. You will most likely wear a vest smaller than what you think.

Sizing for your ThermApparel UnderCool Cooling Vest is really important because it's based on your natural waist. it’s very simple to find your natural waist and you can do it one of two ways.

  1. Stand up nice and tall and bend to the side, where your body naturally creases is your natural waist. Think of the “I'm a Little Teapot” song …”tip me over and pour me out”…right where you crease is where you want to measure.
  2. You can find your natural waist in the area below your rib cage but above your belly button. Right in the center part of your abdomen, in the narrower part where your body naturally narrows.

General Sizing Tips

  • Measure in front of a mirror.
  • Measure on your skin not over a t-shirt.
  • Measure yourself at least 3 times with the same method so that you can get a good average.
  • Sign up for our FitKit for a measuring tape that has our sizing on it, plus tips for getting your correct size and a brochure for info and ordering.
  • Use a fabric measuring tape. If you don’t have one you can use a piece of string a shoelace phone cord and a straight ruler.
  • Avoid using anything that has stretch to it to measure with.
  • You will wear a size smaller than you think.
  • Then check our handy sizing guide and order the correct UnderCool for you.

If you don't have anyway of measuring yourself. 

Sizing tips for Women: It doesn't matter what chest or cup size is. Sizing is all based on your natural waist.

Sizing tips for Men: Go 1 size smaller than your regular fitted t-shirt size.

If you’re between two sizes go with the smaller size. The vest needs to be nice and snug, not tight like it's cutting off your circulation but snug enough that it’s giving you a comfortable hug.

There are two rows of velcro in the front of the vest where it closes so you do have some wiggle room, which is nice if you are between two sizes.

When you get your vest try it on with the packs frozen. Ask yourself these questions.


  • Can I feel all 4 cooling packs on my back?
  • If I had one more row of velcro would it fit better?
  • Is there any space between my back and the cooling packs?
  • Are the cooling packs too low?

Should you go a size smaller?

If you are going to be using the cooling vest  to run, play tennis or use it for any athletic activity where you are bouncing up and down then yes, go with a size smaller.

If you have any questions about sizing please call 855-232-7233, live chat with us on our website or send us an email. We are happy to help.


Sign up for a FitKit

hermApparel is a small business making big waves in the heat sensitivity world by designing the first lightweight, comfortable and invisible cooling vest, UnderCool. Check us out online, on our blog, or on FacebookTwitter, PinterestLinkedIn and Instagram.

Please let us know if you have any other questions or ideas in the comments below, we will follow up. You can always reach us via:
Live Chat -  |  Email -  | Phone - 855-232-7233 |  Address: ThermApparel LLC. 125 Tech Park Dr. Rochester, NY 14620

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