Which type of perm is known for creating a tighter curl?

The correct answer identifies the acid perm as the type known for creating a tighter curl. Acid perms utilize a lower pH, which not only allows for a more controlled and gentler curling process but also results in tighter curls, especially in hair that is more resistant to curling. This type of perm is particularly beneficial for fine or colored hair, as it minimizes damage while still allowing for a defined curl pattern.

In contrast, alkaline perms, while also capable of producing curls, typically create looser and more voluminous results due to their higher pH levels. Digital perms use heat and often result in softer, more natural curls rather than tight ones, and cold wave perms typically involve a similar principle to acid perms but are more commonly associated with a different curling technique and result. Understanding the chemical processes involved in each type helps explain why the acid perm is specifically aligned with the creation of tighter curls.