All materials and animals must enter or exit the isolator through the port (Figure 7.1). The port is a double-barrier system consisting of two caps: the inside cap and the outside cap. The inside cap is solid (no nipples) and in our isolators is held onto the port by 18" × 1" rubber bands. The outside cap has two 1" nipples and is held on the port by a grooved gasket and an 18" clamp. We find the soft rubber band closure for the inside cap and the more sturdy clamp and gasket closure for the outside cap are the most convenient, but any secure method of closure that can be manipulated easily and not damage the equipment will work. The two nipples in the outside cap are for fogging and can also be used to introduce small objects into the isolator. They are sealed by 1" rubber plugs. To introduce or remove an animal or material into or out of the isolator, you must remove the outside cap, surface sterilize the interior of the port, introduce the materials, close the outside cap, fog the port, and then open the inside cap to enter the materials.