Internal liners for concrete containments are generally organic or metals. They have to be able to inhibit radioactive leakage into the environment, but both types have shortcomings. The results of research to develop a better liner are published in this paper. The best material found was fibre-reinforced mortar. Of the fibres considered, steel, kevlar and glass were the best, each showing advantages and disadvantages. 1 ref., 9 tabs., 12 figs.