Originally Posted by
Ziemas
I've got some Mr Tuffy's in my parts box that are over 10 years old and haven't dried out as you describe.
You might also want to look at better tires such as Conti GatorSkins or Schwalbe Marathon Supreme. Both offer suburb flat protection, but I prefer the Schawlbe as they are better in the wet and have a cushier ride.
I don't think they dry out. I think the flexing inside the tire causes them to wear out (I've also heard other people complain of this happening and I myself have noticed it's worse when using ~30 psi balloon tires). I guess stiff, puncture resistant materials are prone to fatigue from flexure.
As to the tires, not all tires are available in all sizes and, in my experience, protection built into the tire doesn't work as well as a separate liner. I think a somewhat mobile layer is more difficult to cut because it is liable to slip from the cutting edge (ie like trying to cut an apple with one hand...not as easy as when you hold it with the other hand).