Agree with mooman76.
Take a pair of calipers or a c-mic and measure the "compressed" thickness of what you are using now, and then take them with you to check material at a fabric store. C-mic is best, but calipers are fine as long as you apply pressure the same when you measure what you currently have and then the fabric at the store. I like calipers with a thumb wheel, the ones without give different readings if you apply decent pressure to them in different spots on the battery case area (digital).
You want 100% cotton or linen. You'll need to wash whatever material you buy to get the sizing out, make sure to put it into a "delicates" bag or nylon before washing or it'll unravel and be a mess when it comes out of the washer. I forgot that part when I bought my first batch...won't forget again.
I have some linen material I bought to try that doesn't shoot well in my rifle, it measures .011" compressed. I read that linen doesn't compress as much as cotton and it was a good idea to buy about .005" under what you really wanted, but I didn't find that to be the case. They just aren't thick enough for my rifle. I'd throw some in an envelope and send to you if you want to try them? I bought the material at a local Joannes. PM me your address if interested and I'll send them. Unless the father-in-law's CVA I haven't worked up a load for yet likes them, I don't have a use for them.