Use of EPS (expanded polystyrene) geofoam as an ultra lightweight fill for construction over areas of soft ground has increased in recent years. An investigation of the interface friction between geofoam and construction materials that are commonly used with geofoam are presented in this paper. The interfaces studied included geofoam to geofoam, in dry and wet conditions. Geofoam to cast in place concrete as well as geofoam to geomembrane interfaces were also tested. Interface strengths between geofoam and HDPE as well as PVC geomembranes were determined. The effect of geofoam surface degradation due to extended exposure to sunlight on interface strength and adhesion bonding with cast in place were evaluated using field samples and samples degraded by accelerated weathering in the laboratory. The results indicate material density; sample size, stress level and surface moisture do not have significant influence on geofoam to geofoam interface strengths. A strong adhesion bond developed between geofoam and cast in place concrete. Both the peak and residual strength for geofoam and cast in place concrete surfaces were much greater than for geofoam to geofoam interfaces. Degradation due to exposure to sunlight and accelerated weathering in the laboratory reduced the strength of adhesion bonding between geofoam and cast in place concrete. The interface strength between geofoam and geomembranes was found to be much lower than any of the geofoam interfaces.