hi torques are phenolic. it's a laminate or layered type of product. not sure what they use, but it could be paper, could be fabric. there are different kinds of phenolic. either way, these aren't ever going to crack apart. they could burn and simply wear out, but won't crack. they're hard also. however, they will absorb moisture.
the black rock rollers were acetal. bad material choice. known to break apart. the newer ones were a PTFE teflon filled acetal, a milky brown color. better choice, but not the best.
two completely different materials in these two products. neither are really a bearing material, but have heard the hi-torques do last.
stock are nylon. extremely tough cheap material. don't hold up to heat well as you may have found out.