NP on the call - UHMW- ultra-high-molecular-weight- (poly-ethylene) or something similar - HA! I bought 2, 2 1/2" thick blocks about 10" square, one for Taylor and one for me. We use it when cutting patches with arch punches - incredible stuff. Your american HDPE (High Density Poly Ethylene) is similar if not identical. Note the white stuff is brand new and that is what is used by the large meat cutting places for cutting table tops. The coloured material, blue or black, yellow, etc, is reclaimed (here) new material scraps, edges corners etc, gone back into the pot, so to speak and is illegal for use for cutting boards.
The coloured HDPE should be cheaper. The two blocks I bought were $10.00 each. I used to get it free in 3/8" and 1/2" thick sheet scrap which I used for firewalls in my radio controlled SPAD airplanes, but not any more. After picking up a batch of 50 pounds or so, I'd take them a 12 pack of beer on Friday afternoon, just before quitting time. That can also work when getting WW from a tire shop- sometimes. Soemtiems they'll 'save' the WW for you. Be aware that California Wheel Weights are now zinc and the addition of a zinc weight into your 10 pound or 20 pound melt will contaminate not only that melt, but your pot's interior as well.
