What is the sizing of these jackets? I went to Surefoot and they only had a Large, which was pretty big/loose. I am a 38" chest and wear small and medium. If I am going to put this over an Under Armour cold weather long sleeve, should I get the XS/S or a Medium?

Tech Specs:

Material:

Aramid mesh, injected polypropylene 

Protection Area:

Chest, elbow, forearm, spine, shoulder, tailbone 

Closure System:

Hook-and-loop 

Recommended Use:

Skiing and snowboarding 

Manufacturer Warranty:

1 Year 

Country of Origin:

China