Irwin Bi-Metal Trapezoid Knife Blades combine the best of 2 metals electro-welded together The edge of the blade is made from high-speed steel which is much harder than standard carbon steel and has been shown to last up to 3x longer in user trials on plasterboard drywalling roofing insulation flooring and other heavy-duty materials The bulk of the blade is made from spring steel which can resist pressure applied from the side without snapping The safest blade to use is generally a sharp one - as it takes less effort to cut and therefore greater control can be maintained This blade stays sharp up to 3 x longer than standard blades The high-speed steel edge and heat treated to greater hardness for longer life and edge sharpness Fit all standard knives