Materials that allow light to pass through them are called transparent.e.g water,clear plastics,shiny glass etc.They do nit cast any shadow.Transparent objects vary in the amount or type of light that they let through their surfaces.Glass is transparent for all visible lights while other objects absorb certain colours and reflect others. Opaque materials: Materials that do not allow light ton pass through them are called opaque.e.g wood,stone,metals etc.They cast a clear and dark shadow.Most materials around us are opaque.Light is reflected ,scattered or absorbed when it strikes them.