What type of curl consists of a rectangular-shaped base that supports a dry design prior to finishing?

The type of curl that consists of a rectangular-shaped base supporting a dry design prior to finishing is known as a barrel curl. This curl is characterized by its large, smooth shape that can create voluminous waves or curls, making it ideal for styling techniques that require body and fullness. The rectangular base helps provide stability during the drying process, allowing the curl to maintain its shape and support the overall design until it is finished.

In contrast, other types of curls, such as pin curls, have a smaller and more specific shape that is typically used for creating tighter curls and waves. Spiral curls are known for their elongated curl shape and provide a different texture, while wand curls are created with a curling wand, resulting in a more natural wave. Each of these styles serves different purposes in hair design, but for the specific characteristic described in the question, the barrel curl stands out due to its unique base structure and design application.