This process takes place relatively slowly as a result of the high energy barrier that must be overcome. Now, what about proteins? Can proteins actually flip flop? Well, proteins have a much higher hydrophilic region, so polar region, than these fossil lipids do. And that's exactly why, if a protein is actually to flip flop, it has to overcome a very large energy barrier much higher than the energy barrier in the phospholipid rotation. And that's exactly why these proteins do not actually flip flop.