controlling warping of PETG        

• Use a heated bed:  Filament manufacturer recommends ideal bed temperatures for each filament. If you’re still experiencing warping after heating the bed, consider printing the first layer hotter and then dropping the temperature for subsequent layers to help with adhesion.
• Use an enclosed print chamber:  An enclosed chamber can be as simple as a frame with a  fire retardant fabric draped over it.
  
• Control room temperature: This is especially important if you don’t want to opt for an enclosed print chamber. Do this by keeping windows and doors closed. (Just remember that you still need air to breathe!) Prevent any cold air from suddenly touching the 3D print.
• Adjust the cooling: Turning off or lowering the speed of the cooling fans directed at the 3D print, at least for the first few layers, may help to even out temperatures enough to keep your model flat on the build plate.

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