What causes paper curl in laser printers?

Here is what HP suggests along with a few of our suggestions to solve problems with paper curl:

• Change the fuser mode (fuser temperature). Many HP Laserjets have the ability to lower the fuser temperature. Consult your user’s manual.
• Store paper in a drier environment. Paper reams generally have a moisture-proof barrier on the inside of the wrapper. Keep the paper sealed until you need it.
• Buy paper from a different vendor or a different manufacturer.
• Print out of a different output bin on the printer, for example a side, top, or rear output bin.
• Flip the paper stack over in the tray or turn 180 degrees.
• Use long-grain paper. You may be using paper with a short grain construction, or the grain might be in the wrong direction.

Some people have made the observation that paper seems hotter when it comes out curled. This is because the paper has more moisture in it. Water does a pretty good job retaining heat; it has a high heat capacity. Heat dissipates more quickly in paper with a lower moisture content. So even though you may be thinking this is a problem of the fuser getting too hot, it most likely is not. Fusers have controlled operating temperatures and if the thermistors in the fuser (the temperature sensors) read too hot the printer gives a fuser error. If the thermistor fails, then a thermoswitch opens up and shuts down the fuser preventing it from getting too hot.