Hint: Instead of a screw-cap, there are plenty of reasons to use cork. Cork is made from bark, which makes it a resource that is sustainable. Plus, the shape of a bottle can be shaped, making it an extremely attractive way to seal the bottle.
Cork is an impermeable, buoyant fiber, a prime subset of bark tissue harvested mainly from Quercus suber (cork oak), which is native to southwestern Europe and northwestern Africa, for commercial use.
Cork is made of suberin, a hydrophobic material, and it is used in a number of products because of its impermeable (airtight), buoyant, elastic, and fire-retardant properties, the most common of which is for wine stoppers. Because of the cork's cellular structure, it is easily packed into a bottle upon injection and expands to create a tight seal.
Additional Information: Cork, the outer bark of an evergreen type of oak tree native to the Mediterranean region, is called cork oak. Cork consists of irregularly shaped, thin-walled, wax-coated cells that make up the peeling bark of birch trees and many other trees, but only the bark of cork oak deserves a cork label in the narrow commercial sense of the term. In Portugal, Spain, parts of southern France and Italy, and North Africa, cork oaks grow abundantly. Typically, the tree is about 18 m (60 feet) tall, with a large, round-topped head and holly-like, glossy green leaves.
So, the correct answer is ‘Air tight’.
Note: To make bulletin boards as well as floor and wall tiles, sheets of cork, also often the by-product of stopper making, are used. The low density of Cork makes it an acceptable material for fishing floats and buoys, as well as fishing rod handles (as an alternative to neoprene).