IMHO I would say material is critical only in the beginning. Once you get the hang of properly varying speed and pressure at the right times then any soft woods work well enough. This is important to note becuase if you psycologically limit yourself to only attempting fire by friction with the very best material then the method is not all that usefull since the very best materials are not always available. However that being said, I agree that while learning, start with the best materials (i certainly did) and once youre getting a coal with them then go on to other materials. Ideally you'd get to the point where you can get a coal from almost anything other than hardwoods.