I really do not know. However, consider that the interior of your car will likely see much more moisture (even if it is just condensation) than the interior of your house will. I would expect that home carpet padding would be much more prone to rot, mold and mildew in a vehicle -- not too mention trapping moisture that will lead to rust in the floor. However, go to a carpet store, and check out what they have available for outdoor carpet padding. That should work just fine.