Acrylic mirrors are a fast and inexpensive way to decorate a room. Acrylic material doesn't shatter and weighs much less than glass, but acrylic material warps easily when exposed to heat. If your acrylic mirror warps don't throw it out, flatten it out and hang it back up.
Remove the backing. If the mirror is in a frame, wearing the safety gloves, gently pull out the mirror from the back with your hands.
Find two pieces of smooth glass that are longer and wider than the mirror.
Place one piece of glass on a protected surface in direct sunlight. Position the warped mirror, reflective side down, on the centre of the glass.
Lay the second piece of glass on top of the mirror. Line up the edges with the bottom piece.
Allow the sun to heat the glass. When the mirror softens and is flat, move the glass sheets and mirror onto a protected surface in the shade until the acrylic material cools and hardens.
Remove the mirror from between the glass sheets. Replace it in the frame and reinstall the backing.
The amount of time required to soften the acrylic depends on the severity of the warp and the heat from the sun. Be patient.
Wear work gloves while handling glass and hot materials. Do not allow the acrylic mirror to get too hot. The heat can damage it, so check on it frequently. To avoid overheating the acrylic material, do not use heat sources like an oven or a hair dryer.