Mylar is mentioned as the only plastic film generally available which is safe for making protective mounts for postal history items. Commercial producers of mounts ought to include information on packages which state the plastic from which the mounts are made, along with data on plasticizers, extenders, residual monomers or other low molecular weight organic chemicals which could diffuse into philatelic material. The greater danger is from the objects themselves on account of the acidity of the paper. Many postal history items are self-destructing and need little or no help from plastic mounts of inferior quality. -- AATA