Objectives: The purpose of this investigation was to determine the thickness of different types of custom-made mouthguards after processing and the deformational changes after simulated occlusal loading. Materials and methods: Ten mouthguards were fabricated for the same dental arch using the following materials and processing techniques: Group I: vacuum-formed (4 mm), Colored Mouthguard; Group II: vacuum-formed (4 mm), Proform; and Group III: pressure-laminated (3 + 3 mm), Drufosoft. After processing, the thickness was measured in three places: lingual cusps of the first molar, distal marginal ridge of the first premolar; and facial of central incisor. The stiffness of each group was determined by applying a simulated clenching force to the first molar lingual cusp areas on an Instron test machine with a blunt probe. The corresponding penetration was measured with a dial gauge. Thickness and force-deflection measurements of the different mouthguard groups were compared using analysis of variance and post hoc tests. Results: The mean thicknesses at the molar for Groups I and II were 1.55 and 1.52 mm, respectively, and were significantly smaller then the corresponding thickness for Group III (3.48 mm). The mean thicknesses at the facial of the incisors for Groups I and II were similar (2.05 and 2.06 mm, respectively), and were significantly smaller than the corresponding thickness for Group III (3.29 mm). Groups I and II demonstrated similar stiffness that was significantly higher than that for Group III. Conclusion: These results show that vacuum-formed mouthguards produced smaller thicknesses than the pressure-laminated mouthguards. The pressurelaminated mouthguards produced material thicknesses that were previously shown to be adequate to protect athletes from trauma. Keywords: custom-made, mouthguard, pressure-laminated, stiffness, thickness, vacuum-formed