So, I have started making my own - cotton at the front, polar fleece at the back. The polar fleece repels the liquid, but is still breathable. The bibs are pretty drool-resistant (lasting for 3-4 hours), but not totally waterproof (eg. if a whole cup of water is spat onto them, some will go through).
longer and shorter length bibs
Here's how I make them:
1. Lay out an existing bib on top of a piece of paper & trace out the shape. Modify it to make a shape you like (eg. I've made some shorter ones for younger babies & some longer ones for older babies). I found it easier to overlock when the top ends were shaped as a point, rather than rounded.
2. Pin your paper pattern onto a piece of thick cotton (eg. corduroy) & cut out the shape. Repeat on a piece of polar fleece.
3. Pin the polar fleece and cotton pieces together and overlock the edges.
4. Hand sew a press-stud at the top.
front (orange corduroy) and back (green polar fleece)