I was getting red marks around my mouth from my mask so I thought this might help. After a week or two of using these liners the redness is gone. I found these things really make the mask more comfortable to wear because the silicone on the mask doesn't pull on your skin. You can also get away with not washing your mask every day which helps save time. I can use each one 3-4 times before they are stretched too large to fit. I would prefer a product that could be washed and re-used. I tried it with these and they have to be ironed after you wash them and then you only can use it once before it stretches again. I also tried a re-usable cover made by someone else, but it was uncomfortable to use, so I will stick with these liners as they aren't too expensive, and it seems like it might help extend the life of the mask which costs even more than the liners.

I'm using a Fisher & Paykel, Simplus mask.

I've been using a CPAP/APAP for about 9 years.
I have extremely oily skin and have problems with a good seal all night. Even if I wash my face before sleep.
This product is great with solving slippage and seal issues because of oily skin. I do think it is a bit pricey though.
It is a bit awkward to place the liner on the mask and it is difficult to replace it if you take off your mask in the dark.
All that said I use these every night and they are comfortable.

Wow, talk about fast delivery! I agree with the other customer who said these should come with all the mask. I was having skin irritation from my AirFit F10 for Her. I have only used the liners for two nights but the irritation is already looking less red. So glad I watch youtube on what to do about rash irritation. Jason (YouTube: TheLankyLefty27) had posted a video about skin irritations and how to solve them, he recommended these liners and the demo was what sold them for me.

My sleep doctor recommended this. I alternate between a medium and a large Quatro FX mask (neither fits perfectly but I sleep better using a medium on the weekend.)
As for finding sizes the RemZzzz site has a page [...] that spells this out quite clearly. Getting Amazon to cough up the large size was a challenge though. Had to page through the options and finally found a box that showed K3-FL, (large) thought the description blurb showed K1-FS (small)
The box of K2-FM (medium) arrived today and I'll be experimenting with how well they work, for both size masks.

Thought someone out there might need help finding the right size too.

After using them for some months..
The medium size works okay with med and large masks. The large size bothers me unless I scotch tape the top to the mask frame, then it stays out of my eyes and lets me sleep. Haven't tried the large with a med mask.

I throw them all in a sweater bag and machine wash them, best if I spread them out on cardboard to dry (as a review suggested) though ironing them flat from a dry wadded up ball isn't too onerous.

I asked BritKare for something that would reduce/eliminate the mask leaks in the cpap mask and they sent me a box of these. Later charged me $85 for them. They work well. Have only "leaked" once in over two months. On Amazon, they were less than $25 for the same thing. Will continue to buy on Amazon. Thanks for the great pricing on a product that actually works.