The difference is the hardness of the silicone, and thus the harder it is the less flexible, but the longer it will last supposedly. I recently tried some of the 60 and that sucks..it's got some flex, but it's also brittle. I tore one mold right in half simply pulling it from the master. The one I like the best so far is the clear 27T. I also bought one of the sample pints of the rubber mold, not silicone, but rubber, I think it's a shore 30 if I recall right. It was super easy to mix up and it looks and feels really nice, but I haven't put it into use yet. I'm thinking with rubber, you will need to wax the mold, but I am finding with silicone you need to wax it too or it just doesn't last long with Alumilite...long being I can get a 100 pours with no release from the 27T and then it starts deteriorating, and I don't consider a 100 pours to be a long time. I am now counting and waxing with the 27 T clear and am now up to 40 pours and the mold is like brand new still.
