There are several online shops that sells protectors for your DE razor these days, mostly made from plastic. You can even download a file to 3d-print your own, if you’re so inclined and have a 3D-printer handy. But did you know that the concept is about as old as the Gillette safety razor itself?

The protector for the cutting edge or edges of the blade comprises shield sides bent over to form pockets for enclosing the cutting edges of the blade when the shield is inserted over the back plate, the blade and the guard. This shield is transversely curved as shown and is of such shape that when the arts are drawn into position for use of the shield may be readily slid into and out of its protective position.

In short, the protector would also serve to keep the head and blade assembly together when the handle was unscrewed completely, thus allowing the blade to be kept in the razor even when the razor was packed away in a travel kit or drawer.