A cap can be configured to engage with cosmetic application devices (also referred to as applicators or cosmetic implements) of various sizes. The cap may include a rigid housing and a flexible body within the rigid housing comprised of elastic material. The flexible body includes a cavity that extends from an opening in the proximal end portion toward the distal end portion of the cap and varies in diameter along its length. The cap may receive an application segment of an applicator through the opening, and the inner surface of the cap can apply pressure to a surface of the applicator to form a seal between the applicator and the cap. The seal between the applicator and the cap protects the application segment from dust and debris and prevents fluid in the applicator segment from drying or hardening.