The technique that creates a croissant’s flaky layers by repeatedly rolling and folding dough with butter is laminating.
During lamination, a baker encloses a sheet of butter inside yeast-leavened dough, then rolls and folds the package several times. Each fold multiplies the alternating layers of dough and fat. The butter must remain pliable but cool; if it melts into the dough, the layers lose definition.
In the oven, water in the butter turns to steam and expands between the dough layers. The fat also helps separate and tenderize the layers, producing the croissant’s crisp exterior and honeycomb-like interior. Croissant dough is laminated similarly to puff pastry, but it contains yeast and is fermented before baking.
A common mix-up is calling the whole process “folding.” Folding is one part of lamination; laminating specifically refers to building repeated layers of dough and fat. The method is also used for Danish pastry, puff pastry and other flaky baked goods. Croissant dough commonly ends up with roughly 16–50 butter layers, depending on the folding method and desired texture.