Triacylglycerol and Cholesteryl ester are

In general, lipids are insoluble in water since they contain a predominance of non polar (hydrocarbon) groups. However, fatty acids, phospholipids, sphingolipids, bile salts, and to a lesser extent, cholesterol contain polar groups. Therefore, a part of the molecule is hydrophobic, or water insoluble; and a part is hydrophilic, or water. Such molecules are described as amphipathic. Water interfaces with the polar group in the water phase and the non polar group in the oil phase. A bilayer of such amphipathic lipids is the basic.