Immunodiffusion Plates are used in Radial immunodiffusion Technique which determine the quantity of an antigen by measuring the diameters of circles of precipitin complexes surrounding samples of the antigen that mark the boundary between the antigen and an antibody suspended in a medium. Immunodiffusion Plates are polystyrene with close-fitting covers to minimize gel dehydration. Plate bottoms are recessed 7 mm to prevent scratching on the bench surfaces. The plate is hydrophilic for easy gel pouring and better adherence to the plate.