This is a simple 'ear saver' design.
This is for use with face masks that use elastic, looped behind the ears.
I've read that the user's ears can become sore if these masks are in use all day.
These are 150mm long and 1.5mm thick.

There are many other designs by other people around, however I wanted a design that keeps the elastic further apart than other designs, is very bendy (for comfort) and uses very little plastic.

The photos show one made from ABS.

Update - I now have some masks. The design seems to work fine.