Red or rough, what makes materials warmer?

The warmth of a material is generally related to the material’s thermal behavior. However, the multisensory experience of warmth is also affected by other material aspects, such as the color or surface roughness. In the current study, we use an experimental approach to investigate the single and combined effects of color and surface roughness on the assessment of material warmth. Participants are asked to evaluate the material warmth of different material samples with controlled colors and roughnesses. The results illustrate that the material color and the local surface roughness influence our perception of warmth irrespective of each other. A relative comparison of the effect sizes shows that a change in color has a larger influence on the perceived warmth than a comparable change in roughness. These results are relevant to architects and other designers wanting to manipulate the intended warmth for a space or building through its materials.