These 18 cell inserts coupled with 10 in x 20 in trays offer you a quick and easy way to carry cell packs to and from your field, greenhouse or growing area. Vacuum inserts are made of polystyrene sheet material. 1801 inserts have 18 single extra deep cells that can be separated. This insert is designed to fit into a 10 in x 20 in nursery flat. These come 100 to a case.