Originally Posted by sweeks

Isn't another reason to use these inserts to make the tires more resistant to flats? A centimeter of foam between the inside of the tire and the inner tube could be significant.
The Schwalbe "Marathon Plus" has a sort of foam insert under the tread, not as thick, but in my experience has been almost 100% effective in preventing flats on my commuter bike.

Cross-section of a Marathon Plus at "autopsy" after a significant failure. This tire had about 3,000 flat-free miles on it.