A unique collection of long term ageing data, this report is an output from the Weathering of Elastomers and Sealants project which forms part of the UK government's Department of Trade and Industry's Degradation of Materials in Aggressive Environments Programme. Rapra Technology has completed a comprehensive natural ageing and physical testing programme on 19 rubber compounds, stored in controlled conditions, for a period of 40 years. This is believed to be the most extensive such study ever carried out.