EC directive 2001/93/EC states that pigs must have permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities. This directive requires further interpretation. In order to facilitate the further implementation of the directive into national, Dutch legislation a preliminary model was constructed to assess the value of different enrichment materials for pigs. Using an e-mail questionnaire expert opinion was elicited in order to `validate¿ the preliminary model. In total 8 senior pig welfare experts assessed 33 assessment criteria ordered according to the conceptual framework underlying the preliminary model. Kendall's coefficient of concordance of the experts without missing values (n = 6) was 0.41 (P <0.001), which is moderate. Assessment criteria that generated the highest weighting factor scores included exploration, animal¿material interactions (AMI), tail and ear biting, and rooting (median expert scores higher than 8.0). The Spearman's rank correlation between the expert median scores and the preliminary model was 0.63 (P <0.001).The scope for modelling and implications for ethical and political decision-making are discussed.