Clay is naturally breathable, the micropores allow for water particles & air to move in & out, naturally self regulating moisture & not growing or trapping bacteria. The top of the bottle is glazed (sealed), to facilitate cleaning the area that comes in contact with the mouth.
To Clean The Bottle
Wash the glazed top with dish-soap. Fill the bottle halfway with water & a dash of coarse salt or water & a tbsp of vinegar, let sit for a few minutes, shake and rinse thoroughly with water.
To Care For The Cap
Periodically seal the wood with oil. Dip a cloth in any kitchen oil of your choice and wipe it over the cap.