The corrosion of metals enclosed in equipment or packages is influenced by vapours arising from other materials which may also be present. Plastics, wood and rubber are the principal sources of such vapours. Even when no vapours are evolved, corrosion of a metal may result from contact with some non-metallic materials. Samples of iron, zinc, copper, aluminium and cadmium either in contact with or in sealed space with various types of non-metallic material, were exposed to corrosion. The extent of corrosion was observed and analyses were made of products and of the surrounding atmosphere. Formic and acetic acid are the most aggressive volatile products from wood and the same compounds, together with formaldehyde, ammonia and halogen acids, may be evolved from plastics and sulphur compounds from rubber. Of the plastics, phenolic resins, especially as mouldings filled with wood flour, and, of the woods, oak, chestnut and beech are the most likely to produce acetic and formic acid vapours, but other materials have appreciable specific vapour or contact effects.