Light cannot go through some materials as they are opaque; these include wood, cardboard and concrete. Other materials allow some light through but you cannot see through them – they are translucent (to some extent). Examples of these include thin paper and frosted glass.
Some materials may fit a number of categories. CD cases are usually made of polystyrene; this can be clear (and transparent) or black (and opaque). A ‘foamed’ variety of polystyrene is also available and is used for insulation and for packing. Polythene is another material that is available in clear, translucent and opaque forms (e.g. clear plastic bags, white bin liners, black bin liners).