Homemade soap recipes make a wonderful gift for friends and family. DIY soap can be easy to make, and it makes a fun weekend project. To make soap completely from scratch (as opposed to melt and pour with premade soap bases), you’ll need to use lye, which is a caustic salt known as sodium hydroxide. The chemical reaction between lye and oil ingredients is called saponification, which creates soap (and leaves no lye in the finished product). Happy soap-making!