Very little MDF contains formaldehyde noawadays. Exterior grade MDF has less than 1% and unless its been sitting for over a decade, the remaining 3 grades should be formaldehyde free.
Dont know if what he got was neoprene or rubber, but the gym matting @dikman mentioned leads me to my suggestion of conveyor belting, or skirting rubber
Its a bit on the pricier side but its usually a natural gum rubber and extremely durable, and dulls abpot the same as the delrin/poly cutting boards.