heat...is caused by friction of 2 surfaces rubbing together ( 2 sticks make a fire theory lol) the faster you file the more friction, the more heat....i suppose e files can cause more heat due to the speed the bit turns and if it isnt been moved around a larger surface ie the whole enhancement, then this will cause alot of heat, saying that a good old 180 file can cause just as much heat if someone files too agressive and keeps filing in one area too long....dont think it makes much difference to either l&p or gel......maybe rough handed ness with l&p is down to application, or gel is softer to file, either way heat is caused by aggresive filing whatever system i reckon