The proteins that are attached to the polar surface and are firmly associated with the lipid membrane are called intrinsic proteins. They are also called as integral proteins. They are relatively insoluble and their dissociation requires rigorous techniques such as the use of detergents.
Some of them may partially penetrate the membrane surface while some of them may penetrate right though. These are amphipathic molecules i.e. the polar “heads” (Hydrophilic) protrude from the surface and the non-polar region is embedded inside the membrane.