Final answer:
In permanent waving for hair, blocking is used to prevent certain sections of the hair from being chemically treated. This technique allows for the creation of different types of curls and waves, providing volume and texture to the hair.
Step-by-step explanation:
In permanent waving for hair, the purpose of blocking is to prevent certain sections of the hair from being chemically treated. Blocking is achieved by using rods or other devices to wrap the hair around, allowing only specific sections to be exposed to the permanent waving solution. This technique helps create different types of curls and waves, giving volume and texture to the hair.