The main difference between the FourSide and WildSide+ jars is size. The FourSide jar is slightly smaller, and the WildSide+ jar has a wider base and larger blade.The FourSide jar has a 3" blade and a capacity of 75 oz (9.375 cups) with markings up to 32 oz (4 cups). We recommend that the finished blended product stays at or below this line. The WildSide+ jar has a fifth side and is designed for larger, faster blends. It has a 4" blade and a capacity of 90 oz (11.25 cups), however, the markings are up to 36 oz (4.5 cups). We recommend that the finished blended product stays at or below this line. There are also two vertical ridges in the jar's interior that allow ingredients to hit two additional surfaces. This accelerates the blending process and makes a smoother blend.