Cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle stoppers, especially for wine bottles. Its low density makes it a suitable material for fishing floats and buoys. Sheets of cork, often the byproduct of more lucrative stopper production, are used to make floor tiles and bulletin boards.
Cork demand has increased due to a larger proportion of wine being sealed with cork rather than being sold in bulk. Since a tree's bark can only be harvested once a decade or so, supply is highly inelastic. Top quality corks are quite expensive, so cheaper brands have switched to lower quality cork, synthetic plastic stoppers, screwcaps, or other closures.
Cork contamination with harmless but foul-smelling trichloroanisole is one of the primary causes of cork taint in wine.
Note that the cork oak is unrelated to the family of "cork trees", which are not commonly used for cork product: