This is a printable adjustable strap for the Prusa Face Shield and derivative designs.  

It is just 2 layers thick and quite strong and flexible. It uses a ratcheting like action with two angled teeth to make it easy to tighten for a precise fit.

Start with the end of the small band un-tucked. Pull the two ends to tighten. Remove from head and tuck the long end into the provided slot.

There are two versions. One is 200mm long for smaller print beds. The other is 220mm long and fits slightly larger heads and has a slightly longer pull tab on the end.

This model prints well in PETG.  It is strong and flexible and works well for this application. When printing, allow the bed to cool before removing. If it hasn't cooled, the material around the notches can deform while removing which prevents it from sliding easily when adjusting.