Cream is the layer that rises to the top in non-homogenised milk. It is made up of a mixture of milk and butterfat. As it is slightly less dense than milk, it floats to the top if it is given enough time to settle. The fat in cream forms quite large globules that can be seen easily with the naked eye. In years gone by this was considered unsightly and was one of the reasons that milk began to be more highly processed and have the cream all mixed in with the milk itself.