What type of implement is acceptable for use due to its porous nature?

The use of porous wood implements is acceptable in certain contexts because their porous nature allows them to absorb some substances, which can help in certain applications, such as applying products during cosmetic treatments. This characteristic makes them beneficial for tasks that require the absorption of liquids, allowing for more effective application of products.

In contrast, synthetic brushes, plastic tools, and metal instruments do not have this porous quality. Synthetic brushes and plastic tools might not absorb products effectively, making it more challenging to achieve a seamless application for eyelash extensions. Metal instruments can also present sanitation challenges, as they can harbor bacteria in small crevices without the absorbent qualities that promote cleanliness and safety that porous wood provides. Thus, in the context of eyelash extension practices, porous wood implements become the best option among the given choices.