Ant, from SecondSkin has the breakdown on this topic--
If I remember what he wrote, it goes something like this--
Peal and Seal & Dynamat are virtually the same product with one very important exception_
Dynamat can withstand temps up to 300 deg. F
Peal and Seal can withstand temps up to about 140 deg F (if that)
This means that after this temp is reached the asphalt compound turns to molten sludge and falls off!
Temperatures in hot dry climates can reach around 150 deg. in the trunk of a car or the door panels.
So if you live in an area where it doesnt get super hot even in the summer, then Peal n Seal probably will work for you without incident.
But if you live in Sunny California like I do, or in Blazing hot AZ like Ant. does, then Peal n Seal will be a risky product to have installed.
One more thing, the other products, like Second Skin, Raammat, Fatmat, and Thunder Audio's sound deadener are all about the same in that their heat resistance is somewhere in the 225-250 deg F. range which is plenty good for even the hottest of climates. The reason these brands cannot approach Dynamat's ultra-high temp resistance is because Dynamat patented the exact chemical proportions in their asphalt mixture.
Ant gets the credit for this one-I think it makes a lot of sense. Hope that helps