The Resmed Mirage Quattro  full-face mask I use is a wonderful  design. It fits snugly and it's quiet. 

It does wear, however, and the part that wears out fastest is the harness. The harness is a nice one-piece design cut out of a neoprene and fleece laminate, with velcro-adjustable straps. 

The hooks of the velcro wears out the loops of the fleece, so that after a time the velcro no longer works. I've successful sewn velcro loop material to the harness, but eventually the neoprene collapsed too. 

After some experimentation I was able to devise a replacement harness out of haberdashery elastic, mylar sheet and a stapler. It is custom-made for me without any adjustability, so any practical implementation will need a measurement scheme. 

Remind me to take a photograph of it and post it here.