Thread-through filter holder for DIY masks

Mostly just for show, since with any effective filter you'll end up A) suffocating B) breathing through the gaps in your mask. Why spend hours 3d printing a mask... when you can sew one in a few seconds? If you use leather, it will be pretty much impervious to virus. A tetrapak carton can also be used, since it will also be 100% waterproof. If you use your old jeans, you should paint it with paraffin to make it waterproof.

All in all, I think just using a 2 layers of non woven fabric and a coffee/vacuum cleaner filter in between will be more than adequate. If you have a old Singer sewing machine, consider learning how to thread it, since the result can be more than 100% better than any 3d printed mask on this site.