Champagne corks use two natural cork discs laminated to an agglomerated cork body. These two discs allow for maximum expansion and provide a tight seal under the high pressure of champagne carbonation.

When the cork is inserted into the bottle, it is straight. The portion of the cork inside the bottle remains compressed by the bottleneck, while the exposed portion expands freely once outside. Over time, as the cork is exposed to the high pressure of the champagne, the compressed inner portion gradually takes on the classic mushroom shape, with the wider, flared top being the portion that sat outside the bottle.