Answer by TDN169. Confidence votes 363. All the molecules in the bilayer are in a low energy state, so are stable on a molecular level. The layer is kept stable because the phosphate head is attracted to the water while the lipid is repelled.This lines up the molecules.They have no reason to move.In a bilayer, the molecules are back to back, so lipids are trapped in a hydrophobic section.he layer is kept stable because the phosphate head is attracted to the water while the lipid is repelled. This lines up the molecules. They have no reason to move. In a bilayer, the molecules are back to back, so lipids are trapped in a hydrophobic section.