This part of ISO 8536 specifies the shape, dimensions, material, performance requirements and labelling for the type of closure for infusion bottles, as described in ISO 8536-1, that is used in connection with the freeze-drying (or lyophilization) of drugs and biological materials. The dimensional requirements are not applicable to barrier-coated closures. Closures specified in this document are intended for single use only. Freeze drying closures can pick up water during shipping, storage, washing and steam sterilization cycles, which is difficult to remove in a subsequent drying cycle. As a consequence, the freeze drying closures are usually loaded with residual moisture. Depending upon the mass of the freeze-dried product and the degree of its sensitivity to water, the residual moisture in the rubber material can spoil the freeze-dried preparation during storage. These specific process requirements have been addressed in this part of ISO 8536 by specifying relevant requirements for freeze drying closures including a test method on determination of residual moisture.