This 3rd layer of polypropylene is now included with my masks.
However, if you want to get more of them, you can do so!
Just insert them through the slot at the bottom of the mask.
Size 1 is suitable for 01/TP, 02/P and 03/M
14 cm x 11.5 cm
Size 2 fits 04/G, 05/TG and 06/TTG
15.5 cm x 11.5 cm
These additions must be washed, just like the mask, after each use.