Interesting build, the author melts down HPDE milk jugs to put into a jig that clamps down make the sliders for a table saw cross cut sled. Me…I have heard dollar store cutting boards work well here too. Also I think I would make a bigger jig to make “blocks” that I could then cut to size.
https://www.instructables.com/Recycled-HDPE-Plastic-Crosscut-Sled-Runners/