You would want a 'stay-dry' fabric, one that wicks the moisture away from your LOs bum and traps it in the microfibre. You can use microfleece or microsuede for this. The microfleece is easiest and is super cheap.
If you want a 100% natural fibre against bubs skin you can use Raw Silk liners - you can buy these as liners from online stores or buy the silk online and cut it yourself.

HTH