The property of cholesterol which allows it to insert itself into cell membranes.

The property of cholesterol that allows it to insert itself into cell membranes would be it being an amphipatic molecule. A molecule is considered as amphipatic when the molecule contains two distinct ends which are the hydrophobic (water fearing) end and the hydrophilic (water loving) end. All of the lipids found in the cell membranes are considered to be this type so that it can allow the passage of the same type of molecule like cholesterol. These molecules are also called amphiphilic molecules. Other examples of this type of molecule are sodium dodecyl sulfate,  Cocamidopropyl betaine,  Benzalkonium chloride and 1-octanol.