Mr S sells chastity cock cages that are made of silicone:
There are two versions, one with spikes, called The Punisher, and one without, called The Boy Trainer. Here is what the folks at Mr S say about this device:
Mr. S carries these all medical grade silicone chastity cages in two styles. You can lock your boy up or yourself, in the Boy Trainer (CB071) and wear it comfortably for days or weeks at a time. The Punisher (CB072) starts to get annoying after a few hours. But stay locked up in it anyway and deal with it. The thick silicone ball splitter separates your balls to either side of the strap beside having your cock locked into the silicone sheath.
Click the pics above to learn more.