What’s the difference between HSS and TCT (also called HM) planer blades?

HSS or High Speed Steel planer blades are sharper, which gives you the smoothest planing result. TCT (Tungsten Carbide Tipped) blades, also called HM (Hard Metal) blades, are less sharp. They give a slightly less smooth result than HSS blades, but the result is still very good. The big advantage of TCT blades is that they stay sharp up to 5 times longer.