Sleep pad? What's a sleep pad?
Use a bunch of pine boughs and some leaves, rake the leaves up with a stick, make a pile as long and wide as you need. Make it thick enough so that it is 4 fingers thick when compressed. Better insulation, a lot softer, will probably smell better. Definately cheaper. Don't have to worry about punctures. What's not to love?!
One, can't tear apart trees where I camp. Two, it would tear up my tent. Three, it would tear up my sleeping bag.