After getting a flat on three out of three rides on my mtb (lots of briars around here), I decided I needed some sort of protection. the lbs was out of slime tubes so I decided to try a Slime tire liner. It's a lightweight liner that protects the tube from puncture through the tread, won't help for sidewall or pinch flats. They guarantee it for flats from tread punctures and will replace the tube and the liner if you send it back to them. So far, so good!