A trim cut is when you remove a cut an extra (1/8”-1/4”) on the outside of your mold while you're cutting on each side of the soap while cutting. There are two reasons for trim cuts: Clean bars: The sides of soap loaves/blocks can look rustic due to the mold’s lining. Adding a 1/8”-1/4” trim on the sides of your soap will leave perfectly smooth sides on all of your soap bars. No lining: A trick some customers use to avoid having to spend time lining their molds is to use a trash bag or plastic bag as the liner, then add a trim cut to fix the side walls. Trash bags make the sids of your mold look rough, but once you trim cut the sides it's a perfect square with no wavy lines. The downside to trim cuts is that you might get fewer bars per mold (depending on bar size and mold type), and you also lose a (small) amount of material when you're making the cut.