Seat belts are made of woven fabric, nylon I think. The weaving will allow thorns, small brads/nails to slip through. I don't think it's worth the time and effort to use them. Bike shops sell a strip of mono-molded polyethelene in rolls that fits between the tire and the tube. it comes in several widths so should fit most tire sizes. It is very tough stuff and I had quite a time working a brad through it, I can see where it would stop almost anything sharp trying to flatten your tires.