It was hypothesized that the perceived enclosure effect of spaces would be dependent upon the explicitness of presented architectural surfaces according to the 1961-1970 model of Thiel. It was also hypothesized that the contribution of the surfaces would adhere to theoretical weights proposed by Thiel. It was further hypothesized that the perceived contribution of the surfaces to enclosure would be similar for men and women. 20 women and 10 men were presented 24 line drawings in one-point, eye-level perspective of the same furnished and occupied interior space. The line drawings differed only in the absence or presence of floor, wall, or ceiling surfaces. On an initial task the spaces represented by the drawings were ordered by the subjects from least enclosed (most open) to most enclosed (least open). In a second task the surfaces in a diagram were ranked according to their relative importance in determining the perception of the enclosing effect. The hypotheses were confirmed, and so provided support for the model that the explicitness of perceived surfaces contribute differentially to the perception of the openness of an environment.