It is hydrophobic as a result of those hydrocarbon tails. And what that means is for a molecule to actually be able to pass across the cell membrane, it must be able to dissolve inside the core of that phospholipid Bilay. So that implies that the permeability of a molecule depends on its ability to actually dissolve in a nonpolar hydrophobic solution. So the more nonpolar a molecule is, the more likely it is to actually dissolve within the hydrophobic core environment of that phospholipid bilayer membrane. So what that means is for a nonpolar molecule, for a small non polar molecule to actually pass across the cell membrane, it basically dissolves inside that cell membrane as it moves across that cell membrane. And to see what we mean by that, let's take a look at the following diagram.