These trays perfectly fit the PP-391 hatching drawer and provide a cushioned liner for the eggs as well as firm footing for newly hatched chicks. These liners are 2-ply heavy paper. The top ply has been treated with a mild germicide to control bacteria and suppress odors. Highly recommended, these disposable tray liners make for a quick and easy clean up of the plastic hatching drawer in the PP-391 and PP-418 incubators. Liner size 13.25 X 27.69.