You can use towels in the middle. Or cut up mattress protectors. Those are what I use in my cage liners.
They would work in piddle pads too. If they really wee a lot in some areas (like houses) then maybe double up the inner layer. If it's just the odd widdle here and there then a single layer of mattress protector or perhaps double layer of towel would be fine.
I have also made some with chamois in the middle. The kind sold for cleaning cars etc. I know some go really hard when dry, but the ones I bought stay nice and soft like cloth. I walked around the hardware store randomly browsing and saw them hanging there saying how they absorb 10 x their weight in liquid so figured they'd work well, and they do.
Old fashioned cloth nappies (terry squares) would also work, perhaps best if folded double.
Face cloth too.
Perhaps even a dishcloth folded double.
Anything absorbent really.
You can make them with fleece on one side, absorbent layer in the middle, and a waterproof layer on the back, or you can make fleece on both sides and absorbent layer in the middle.
I have made both and honestly I prefer the ones with fleece on both sides. My piggies mostly wee in their litter tray, just the odd widdle in their houses, so I like the double sided fleece ones best because then I can tip the poos off, dust off any pellet dust, and turn them over for a clean top. Kind of get to use them twice before washing (I always check to make sure they don't feel wet).
