A rigid receptacle in which impression material is placed. Materials commonly used for impression trays are metal, shellac, or resin. They are usually coated with tray adhesive immediately prior to use and may be perforated with 2–4mm diameter holes or made from metallic mesh to improve the adhesion of the impression material to the tray. Stock trays are rigid trays commercially manufactured in different sizes and shapes and usually made of resin or metal. Edentulous stock trays have a shape which conforms to the shape of the edentulous ridge of either the mandible or maxilla. Dentate stock trays have a box shape to accommodate the teeth in the arch. Custom trays are made from a primary cast and, because their shape conforms more closely to the shape of the teeth and tissues to give a more uniform thickness of impression material, it provides greater dimensional accuracy. Custom trays are usually made from shellac or resin. A sectional tray is used to take an impression of a specific area of the dental arch such as a quadrant or sextant.