Environmental enrichment is important for animal welfare, as farm animals are often kept in barren environments (e.g. Young, 2003). In 2001, the European Commission adopted a directive (2001/93/EC) which states that: ‘‘Pigs must have permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities, such as straw, hay, wood, sawdust, mushroom compost, peat or a mixture of such, which does not compromise the health of the animals’’. This directive has been implemented in most EU member state’s legislation; however, a problem with the directive is that it is not clear. For example, it does not explain whether metal chains, ropes, rubber toys or hard plastic balls are sufficient materials to enable proper investigation and manipulation activities. In addition, the value of an enrichment material is most likely determined not only by the type of material, but also by other properties of the material such as the amount and frequency of material provision. A model, called RICHPIG, has been developed to calculate scores for the (relative) enrichment value of different materials from the point of view of the animals. In the model a number of benchmark treatments have been incorporated. These benchmarks do not only illustrate how the model works, they also provide a frame of reference for the assessment of new treatments. A preliminary version of RICHPIG was used to calculate scores (on a scale from 0, worst, to 10, best) for a set of enrichment materials and subsequently experts were asked to evaluate these materials and the model scores. This generated a first validation of the model, which can always be developed further as it has been constructed in a flexible format where information can be added when it becomes available. It serves as a statement regarding how internationally recognised experts assess enrichment materials in relation to proposed model scores, given the present state of science. The aim of this paper, therefore, was to examine expert opinion concerning enrichment materials for pigs and to determine how their scores relate to preliminary model scores. Using an e-mail questionnaire expert opinion was elicited in order to ‘validate’ the preliminary model. In total nine senior pig welfare experts assessed 64 enrichment materials ordered according to the preliminary model. Materials that generated the lowest scores included a mirror (attached to the wall), a concrete block, a rubber mat, straw at an absolute minimum, a mineral block, a heavy plastic ball, a chain, a rubber hose cross, a free toy (sow neck tether), a hanging car tire and a bucket (all median expert scores). Materials that generated the highest scores included whole straw with chopped beet roots, with maize silage or with additional feed, a bale of straw, long straw with fir branches and straw with forest bark and branches. Materials that the experts suggest as the minimum of what they consider acceptable enrichment included compost from a dispenser, straw pellets (loose or from a plastic dispenser) and straw in a metal basket. A high correlation was found between the preliminary model scores and the expert medians. This finding was confirmed in a workshop at an international conference, suggesting that there may be considerable scope for modelling to support ethical and political decision-making in the area of environmental enrichment for pigs.