Butyl is rubber. Asphalt.. is well.. asphalt.

How to tell them apart? Hard to do. I mean you don't want to light your doors up right?

Best bet is to simply start by purchasing stuff that you're sure is made of butyl.

Based on your posts dito sa tsikot and sa KAC. Di ko talaga alam if your installer is recommending you for a second layer (Tsikot) or not (85% na daw yun one layer -- KAC).