Frost retardant of glass fiber (GF)/unsaturated polyester (UP) composites was evaluated with surface roughness. Glass fiber reinforced composites (GFRCs) were manufactured, using 8 ply fabric type GF mats and UP at 50 vol% volume fraction, using a vacuum assisted resin transfer molding (VARTM). Surfaces of the GFRCs were sanded using different grit sand papers. Static and dynamic contact angle (CA) measurements were performed to determine the hydrophobicity of specimens with different surface roughness. Observation of frost thickness versus time was performed to evaluate frost retardant as a function of surface roughness. An atomic force microscope (AFM) was used to quantify the surface roughness produced by sanding with different grit sand paper. It was found that surface roughness, CA and frost formation thickness were all-dependent on the grit of sand paper used in the sanding process. These behaviors appeared to be interrelated with an optimal sanding grit size of 320 CC. (C) 2018 Elsevier Ltd. All rights reserved.