Traditionally, according to materialists, culture is a representation of outer reality. Culture is considered an accurate method of analyzing the material world as it accurately depicts the outside world and its traditional aspects.
Cultural materialism is different from this traditional viewpoint. Culture is considered as part of the material world. Culture is regarded as a human activity in society as it includes how we organize our lives rather than how the world is represented through music, literature, and art. For example, the houses humans construct and how people relate to each other should be deemed cultural since they are part of (rather than how they reflect) material reality.
Traditional materialists examine the difference between social reality and cultural perceptions relating to it. Cultural materialist considers this social reality itself as culturally constituted. Culture is an energy that creates the material world rather than reflects or expresses it.
Critique is difficult to impossible in cultural materialism as to criticize culture one has to refer it to a world that is external to it.
Reference : John Hoffman