This underlayment is a better product than Firestone. From an install perspective the Firestone is slippery, and takes time to dry before they can work on the roof or they have to hand dry it. The FT product is thicker, not slippery, some insulation value and can handle more abuse from the sun and rain. I have a roll from my solar roof install which I will use on my shed, it would outlast the home depot shingles by 10 years!