Acrylics are available in a range of colours and can be opaque, translucent or transparent. They are available in sheet, rod, and tube for use in injection moulding, extrusion and vacuum forming. Acrylics withstand weather and are stable in sunlight. Almost any colour can be produced. Transparent acrylic can be as clear as the finest optical glass, this led them to be used in optical equipment such as cameras. It is possible to significantly strengthen the acrylic when it is being made, these high grade acrylics are used use for aircraft windows.