Several studies have shown that straw provides an outlet for the foraging and explorative motivation of pigs and that the provision of straw reduces abnormal manipulation of pen mates (e.g. Bolhuis et al., 2005). Alternatives to straw have also been investigated, for instance peat (Beattie et al., 2001), which was found to have the same beneficial effect as straw, and which was preferred to straw (Pedersen et al., 2005). Various so-called ‘toys’ have also been suggested as rooting materials. The pig producers may prefer the toys, because they do not interfere with the slurry system, but pigs prefer chewable toys to more ‘durable’ toys (Apple and Craig, 1992). Furthermore, straw bedding (Guy et al., 2002; Van de Weerd et al., 2005, 2006) and mushroom peat (Beattie et al., 2001) are the only rooting materials that have been reported to reduce tail biting. The rooting materials must enable the pigs to perform investigation and manipulation, and the literature suggests that materials that are complex, manipulative and edible (Van deWeerd et al., 2003; Olsen et al., 2000) stimulate the most investigation and manipulation. In a recent study Pedersen et al. (2005) developed a method using concurrent schedules of reinforcement to assess the strength of pigs’ preferences for different rooting materials. When animals work on concurrent schedules of reinforcement for food, or other valued resources, they adjust their efforts according to how difficult it is to get access (the workload) to either of the two resources and the quality (the value) of the two resources in relation to the underlying motivation. Based on the trade-off between workload and value we can calculate how much more they value one resource relative to the other. The aim of the present experiment was to assess the relative value of six rooting materials based on the cross point between demand functions derived using concurrent schedules of reinforcement. Twelve pigs were tested with all six combinations of the reference material (peat) and one of the six test materials in a balanced design. The cost of access to both reference material and test material was varied. For each combination, demand functions for both materials were estimated as a function of the cost of the reference material leading to a cross point of the two demand functions. The cross points revealed the following ranking (the lower values are the most preferred): maize silage with straw (14.2 (9.5–18.5)), spruce chips (18.0 (13.8–21.9)), compost (18.2 (13.8–22.3)), sisal rope (25.5 (21.4–29.6)), seed grass hay (27.1 (22.7–31.8)), chopped straw (28.5 (24.5–32.8)). All the tested materials were valued as much as chopped straw, but maize silage with straw, spruce chips and compost were valued higher. The results confirm that pigs prefer more complex and compound rooting materials.