It is made up of two layers, each composed of a lipid bilayer. It is perforated with holes, called nuclear pores, to facilitate and regulate the exchange of materials (for example, proteins and RNA) between the nucleus and the cytoplasm. In between these two membranes is a space called perinuclear space. The outer membrane is continuous with the endoplasmic reticulum. The inner membrane is associated with a network of intermediate filaments called nuclear lamina, which is made of lamin. The lamina acts as a site of attachment for chromosomes. It also acts like a shield for the nucleus.