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!


General Sizing Tips:

  • Sizing is based on your natural waist, not your hips or pant size. 
  • Cooling Products needs to fit your body like a glove to give you the best cooling support. 

UnderCool 3 Sizing Guide

3.0 Sizing Tip: If you are in between 2 sizes order the LARGER size. 

Size Natural Waist
Extra Extra Small - XXS  18" - 24"

46 cm - 61 cm


 24" - 31"

61 cm - 78 cm

 31" - 40"

78 cm - 101 cm

 40" - 51"

 101 cm - 129 cm
Extra Extra Large - XXL 51" - 64"

129 cm - 162 cm

UltraCool Sizing Guide

Size Natural Waist
M/L 32"-45" 78cm-101cm
XL/XXL 45"-65" 101cm - 129cm

RallyWrap Sizing Guide

The RallyWrap is one size fits most.  If you would wear an XL Tee Shirt size, we recommend getting your RallyWrap with 8 Cooling Packs so that the cooling will wrap around your entire torso.


Using a Fabric Measuring Tape:

  • Sizing is dependent on natural waist size not bust size.

1. Stand or sit 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.

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.