Permeability theory suggests that perceived enclosure should be mitigated by the walkability of the surface underneath a person. This prediction was tested by obtaining ratings of perceived threat, perceived walkability, and perceived enclosure for five types of surfaces: pavement, grass, sand, water, and rocks. There were three experiments, 20 stimuli, and 112 participants. Perceived threat and perceived enclosure were highly correlated, as were perceived walkability and type of surface underfoot. Environments in which the surface underneath were difficult to walk over were perceived as being more enclosing and more threatening than surfaces that were easy to walk over. The findings all supported a priori hypotheses generated from the permeability theory of environmental perception and preference.