It doesn't require a vapor barrier. Its definately the best insulation out if you can afford it. Fire prevention. You just touch it with a torch and look out.:no: This is why you don't ever want to spray under floors where there is copper piping. If A plumber pulls out a torch to sweat a pipe connection and just touches the insulation. Its all over with. You wouldn't believe how quick that stuff will go. The hole thing will be on fire and he won't be able to contain it.Guarantee means, does it effective for preventing moisture, fire etc.?