Lipid have long nonpolar chains of carbon atoms which adversely affects its solubility in water. Thus, they are insoluble in water because they are hydrophobic.
Related Theory
Allofthelipidmoleculesincellmembranesare amphipathic that is, they have a hydrophilic or polar end and a hydrophobic or nonpolar end. The most abundant membrane lipids are the phospholipids. These have a polar head group and two hydrophobic hydrocarbon tails.