An investigation into the reflection of acoustical transients from a surface of Fibreglass has been carried out, with an electrical spark used as the transient noise source. The Fibreglass was backed by chipboard. The transient field was measured for various source and receiver positions above the surface. A computer simulation of the experiments, with both spherical and plane wave modelling of the reflection process, proved to be adequate to predict the sound field for source and receiver geometries where the angle of incidence of the wave was less than about 60 degrees. In these simulations surfaces of both local reaction and extended reaction were investigated.