Cushion Plastic Material?

Does anyone actually know what the cushions of most masks are actually made of? I know everyone says 'silicone', but there has to be more to it.

I have multiple masks, each pushing roughly about the same age, near 5-8 months. Several cushions, even though they all have been washed after each use and stored in the same dresser drawer, have started to faintly yellow. Plus, the ancillary parts, like the air valve(s) and oxygen port plus are also yellowing. The cushions seem to be holding the seal pretty well, it's just they are yellowing.

One mask, however has remained clear.

So are some masks silicone blended with other plastics or lower grade silicone that yellows at a certain age? Kind of like the toothbrushes with the blue "indicator" bristles?

This is becoming a mystery.....

my digging on the internet shows that a lot of mask frames are made of a polycarbonate material.... all the standard cushions are listed as either "silicone" or "Soft Silicone". I've never been able to find out the exact type of silicone used

Everything I have read shows that silicone will yellow due to exposure to air or sunlight.

The new resmed directions for the Quattro AIR state several times to keep the cushion out of direct sunlight. As well as not washing it in temps above 86 degrees F

When I store slightly used cushions, I wash and dry them and then put them in ziplock bags and squeeze as much air out a possible.

I've had some parts like the oxygen piece on my Quattro turn slightly yellow... I washed in the dishwaher with it in the utensil basket and quite a bit of the yellowing was eliminated

Mask parts will yellow with age even if still in original sealed from manufacturer package. Not as much as when open to the air. I have several various mask parts from the donations that are still in sealed packaging but they have aged a bit yellow with time.

I found a new but opened nasal pillow in one of my dresser drawers a while back. Must have been in there well over 6 months. It was just tossed into the drawer...no bag. It was a real nasty yellow brown color. Brand new but look like Hell.

Almost all cushions are different grades of silicone. There are some old masks that were designed with Vinal but that was a long time ago. They will age differently in your hands because you dont know the actual manufacturing date. Those cushions could have been sitting in warehouses from the OEM or in the sleep lab's stock shelves for a while. All Silicone eventually yellows with age, there is nothing added to the silicone to do that.

Maybe impurities?
We know that silicone has a tendency to absorb gases for the lifetime of the material.
This may be why it is so difficult to get odors out of a cushion (cigarette, anyone?)

FWIW, my older Swift FX pillows yellowed very quickly where they contacted the black
rubber O-rings I added for stability. This has not happened with newer pillows with
the same O-rings.

First off, you are asking someone to reveal a trade secret. The formulas used belong to each mfg'er.

That said, I used to work for an expoxy and urethane mfg'er; we also weaved our own carbon/kevlar fiber, back in the late 80s/early 90s. Part of my job was purchasing medical grade silicone for use in some of our products. Products ranged from skate board wheels to heart valves. We just made the liquid; part A & B and we had some one component product that cured at room temp.

If I remember correctly, none of the medical grade products were our own. A large medical firm owned them and used our plant for mfg. We had one small vessel designated for medical products only. In at least in one case, the medical firm would supply 99% of the chemicals. Quality Assurance went thru our internal lab and their lab both prior to shipping and after delivery.

The color change (yellowing) is probably due to a lack of UV stabilizers in the formula.


(sorry for the double post -- deleted)