This is something new to me.
How much weight would the gel add to the bike?
SLIME Tire Sealant
It's amazing stuff. Here, there are tons of goathead thorns and they can cause multiple flats in just a few short meters.
Slime in the tubes will patch small holes from the inside. It's a viscous material with small fibres in it. It's really amazing stuff, just don't get it on your skin as it can cause a skin reaction.
I've used slime for the past year and along with my Schwalbe tires, have not had a flat in 14 months. I am totally car free, so my bicycle gets daily use. I can't sing the praises of Slime and Schwalbe enough!