A simple strip to secure a facemask. The design aims to:

• Allow using non-elastic bands (since those are currently low on supply)
• Make it more comfortable to wear it by taking the strain off the ears
• Allow leaving the mask around the neck when it is not needed

There are currently 6 sizes, which one fits your head/mask best is a bit of trial and error. I took a paper strip to measure the gap of the bands behind my head and then went from there. If you have a mask with elastic bands, probably any size will do and the only difference will be how tight the mask sits on your face.
If you wear it with the band above/around the ear, 13-15cm should be fine. If you wear it with the band below the ear 8-10cm should fit.

Edit: Made some modifications to give it more springiness and make it harder for the band to slip out.

If you want to make modifications, you can use my onshape project and modify it to your liking:
https://cad.onshape.com/documents/c1402a81c716c3e38e73b052/w/76b6c42d07dae67320a01da9/e/d25dcdad021d076cbf9ef342

Creality

Ender 3

No

No

0.24mm

Irrelevant

You may want to use a small brim if you have sub-optimal bed adhesion

You should check for sharp edges and remove them to ensure not to damage your masks bands.