Most designs of disposal facilities for higher toxicity radioactive wastes were developed for generic feasibility assessment and hence tend to be rather simple in terms of layout and conservative in the choice of engineered barrier materials. Recently, there has been a trend to reassess such designs in the light of moves towards implementation, where robustness in terms of post closure safety needs to be balanced against the requirements to assure safety, quality, and economic practicality during operation, to minimise environmental impact and to gain public acceptance. Studies to date have, however, tended to focus predominantly on variants of layout and engineered barrier geometry. Evaluation of alternative materials has received less consideration, despite the huge advances in materials science over the last couple of decades and likely further developments in the time until repositories become operational. This paper will examine the constraints that led to the choice of the most common materials selected for barriers within “wet” host rocks and examine the extent to which performance could be optimised by use of alternative materials.