Orders placed before 3pm EST (Mon-Fri) ship out same day! WOW!

How to get the right UnderCool for you.

Need Help With Sizing? Fill Out the Form, Get a Free FitKit.

The ThermApparel Fit Kit is loaded with tips and suggestions and a handy measuring tape so you will get the correct size when you order. Fill out the form below and we will send you a FitKit!

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UnderCool Sizing Guide

Size Natural Waist
Extra Extra Small - XXS  20" - 24"

51 cm - 61 cm

Extra Small  25" - 28"

 61 cm - 71 cm


 29" - 34"

71 cm - 81 cm

 35" - 40"

 86 cm - 97 cm

 41" - 46"

 102 cm - 116 cm
Extra Large - XL

 47" - 55"

 121 cm - 132 cm
Extra Extra Large - XXL 56" - 61"

140 cm - 152 cm

Sizing Tips:

• Sizing is based on your natural waist, not your hips or pant size. 
• Measure against your skin.
• Take your measurements in front of a mirror.
• Make sure your tape measure is level on both sides. 
• UnderCool needs to fit your body like a glove to give you the best cooling support. 

1. Stand up
straight and tall.

2. Bend at both sides.
Where you naturally
bend in your natural

3. Measure where you bend.
If you don't bend measure below rib cage but above belly button.

Womens Sizing Guide:

Sizing is dependent on natural waist size not bust size. You will wear a smaller size than you think. 

Men's Sizing Guide:

We recommend ordering a size smaller than your usual T-shirt size.
(If you wear a large T-shirt, a medium UnderCool will fit best.


Don’t Have a Fabric Measuring Tape?

You can measure your waist the same way with a straight ruler and:
String / Yarn
Dental Floss
Charging cord from your phone


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.