I was looking for a vendor for these jspacers for the longest time. I'm glad I was able to find them here.
It's a bit hard to tell from pictures but they are a rubbery like material which silences the keypresses. While you can tell the j-spacer is rubbery from the feeling on the switches, it isn't a mushy feeling that silicone o-rings might give.
As stated in the title, I was able to make a batch of 25 jailhouse blue outemu switches and each switch felt identical to one another. When using other materials like floss, wire, dental bands, or o-rings, there was always enough variation for some switches to fail after extended use. Which is quite annoying.
These are well worth the price.