Modeling laser transmission welding of thermoplastics requires knowledge of the optical properties of the two materials being joined. Previous work measuring optical properties for this purpose placed little importance on the light reflection, emphasizing the light transmitted through a material. This paper presents work creating a low-cost solution allowing simultaneous measurement of the light transmission and reflection of clear rigid poly(vinyl chloride) from a diode laser source. Total reflection is quantified by numerically integrating measurements of the light reflection at specified locations around the perimeter of a sphere surrounding the sample; simultaneously the light transmission through the samples is measured. From a designed experiment involving two factors—surface finish and material thickness—the absorption coefficient of clear rigid poly(vinyl chloride) was calculated. In addition the quantity and distribution of light reflection was found to be dependent on the surface finish.