You can easily fit an air mattress inside your car because it tends to be adjustable or bendable to adapt to the size of a car’s interior. If you need more padding, you may add an underlayer of closed-cell foam mat under your insulated sleeping pad. Otherwise, you can stack two sleeping pads together to double their insulation and cushioning capacity. If you need a wider sleeping area because you’re family camping, snap two sleeping pads together if you’re pad has built-in snaps like the KAMUI self-inflating sleeping pad.