Answer:
They have hydrophilic heads and hydrophobic tails.
Explanation:
Phospholipid membranes are comprised of a chain of lipids. These typically are arranged in a bilayer; the hydrophilic lipid heads are polar, and face outwards, while the hydrophobic tails are polar facing inwards.
The membranes are selectively permeable, and only allow the movement of small, non-polar molecules through the bilayer.