Phospholipid molecules usually have hydrophobic tails and a hydrophilic head. Biological membranes in eukaryotes also contain another class of lipid, sterols. These are spaced out among the phospholipids. Together they provide membrane fluidity and mechanical strength. Purified phospholipids are produced commercially and have found applications in nanotechnology and materials science.
- Introduction to lipids. Carnegie Mellon University. 
- hydrophobic = water-rejecting; hydrophilic = water-loving.
- Mashaghi S; Jadidi T. & Koenderink G. Mashaghi A. (2013). "Lipid nanotechnology". Int. J. Mol. Sci. 2013 (14): 4242–4282. doi:10.3390/ijms14024242. http://www.mdpi.com/1422-0067/14/2/4242.