The expansion chamber, not the muffler. I cut open the pipe to fix a dented section from hitting a tree Thursday and noticed that it had a perforated inner layer with what appeared to be fiberglass mat between it and the outer chamber. Has anybody cut this out and is it there for sound deadening only? Back in the day I helped a buddy gut his stock KDX pipe (which had way more baffling-then again the pipe was bigger too) and it made a significant increase in top end power, but it also made it kinda pipey.