Caffelatex 250ml Foaming Synth Latex Tire Sealant
Caffelatex is a truly innovative tire sealant: the first of its advantages over standard latex-based sealants comes from a foaming agent (Actifoam), activated by wheel movement. Centrifugal force drives standard latex-based sealants against the outer circumference of the tire.
Caffelatex foaming action causes it to fill the tire's entire internal cavity, making it much more effective against sidewall punctures.
I had this put in when I my 29er was built. There was about a baseball sized glob that formed in my front tire.