The study looked into the effects of interface modifications on the tensile properties of glass microsphere filled polypropylene. The interface was modified by the use of two different silane coupling agents at different loading levels. This was performed to manipulate the interface and examine its effects on tensile properties. The two different silanes used in this study were: methacryloxypropyltrimethoxysilane (methyl silane) and a vinyltriethoxysilane (vinyl silane). Fourier Transform Infrared Spectroscopy (FTIR) microscopy was utilized in an attempt to measure the characteristics of the interface and draw comparisons to the tensile properties exhibited. It was observed that generally as the percent silane increased, the elongation of the composites decreased.