Speaking of longevity, I made this silicone mold way back in mid-2000.




Last time I checked it maybe 5 years ago, it looked "not bad", now it's got a slimy feel, and the main bulk has shrunk relative to the 3 small partitions. I'd say it was good quality for at least 10 years.

I don't know if Smooth-On has "watered down" their products by now, but I can guarantee they were awesome when I was playing with this stuff.

I also tested one of the liquid plastics that you can make threads. All I remember is that it was graded industrial strength, and was mixed by volume, 50-50 (I didn't have a digital scale back then and didn't want to be bothered with them).