What they are ............a silicone sleeve a bit thicker than a condom, usually with bumps or ticklers (french) that fit over the shaft. They come anywhere from 2-4" in length.. It would squeeze the shaft enough (spreadout) between scrotum and head to prevent turtling in the flaccid state.
I've pasted a link at one particular adult store online. I in no way am pushing this product or promoting this site but rather showing you an example of what is available.
Big Sex Toy Store - GK14033 - Six Piece Sleeve Set