The nuclear envelope , otherwise known as nuclear membrane , consist of two cellular membranes , an inner and an outer membrane , arranged parallel to one another and separated by 10 to 50 nanometres ( nm ) . The nuclear envelope completely enclose the nucleus and separate the cell 's genetic material from the surrounding cytoplasm , serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm . The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum ( RER ) , and is similarly studded with ribosomes . The space between the membranes is called the perinuclear space and is continuous with the RER lumen .