Whilst the uptake of sustainable interior design has increased recently, material selection has improved only slightly since the mid-1990s. This is probably because human values and attitudes have not changed significantly, despite the prominence of sustainability in government policy. This paper describes the results of a research project that investigated the sustainability values of interior designers and examined how those values shape designers’ behaviour, particularly the selection of materials for design briefs involving sustainability. The project categorised designers into three groups according to their sustainability values: champions, conformists or challengers. A set questionnaire was used in interviews with 20 interior designers in Sydney, Australia to determine how they perceived their own sustainability values. They were categorised into the three value groups, and the relationship between their perceived values and behaviour was analysed. Analysis showed that the designers’ perceived values were not necessarily transformed into behaviour; that the value groups took up ecomaterials at different rates; and that the groups had different levels of knowledge about sustainability. These results help to explain the disappointing uptake of sustainability in interior design and might suggest possibilities for effecting change in this area.