Is one side a mylar type material?

Heatsheets are made from coated polyethylene. That's what makes them superior to the mylar Space blanket that punctures and tears easily. Also, Heatsheets have one side that is colored, so you'll always have the silver side that provides for 90% reflective insulation towards you for warmth. The Space blanket is silver on both sides, so you have a 50% chance of getting it wrong!

I have the emergency bivy that is similar to this, and mine is a sort of tyvek-like material, very tough for the weight.It feels kinda flimsy, but it'll do the jobThis one will work just fine by reflecting your body heat back. I've been using the ACR for years & it's lighter:http://www.backcountry.com/store/ACR0012/ACR-ThermaBlanket.html