Abstract: A sheet material decurling apparatus for use with a machine having a sheet conveyor comprises a trough member which includes two elongate, sheet supporting members, each having an arcuate upper surface with a radius greater than 250t, where t is the thickness of the sheet material. An elongate fillet, curved in the direction opposite to and joining the sheet supporting member surfaces, has a radius less than 15t. Further, the angle formed between the planes tangent to the sheet supporting member surfaces at the lines of transition therefrom into the fillet is in the range of 60.degree. to 120.degree.. A series of vacuum conduits are disposed in the trough member adjacent the bottom of the fillet and have a total cross-sectional area of approximately 0.07 inches square per linear foot of trough member. A vacuum pump is connected to the vacuum conduits to effect air flow downwardly through the trough member.