Plywood is a building material made by gluing thin sheets of wood together in layers, with each layer's grain running perpendicular to the ones above and below it. This crisscross pattern makes plywood much stronger than a single piece of wood of the same thickness.

Imagine a stack of papers where each sheet points a different direction: that's essentially how plywood works, except with wood veneers (very thin slices of wood). By alternating the grain direction, plywood resists splitting, warping, and cracking far better than ordinary lumber. A piece of regular wood might crack easily if you try to nail near its edge, but plywood holds together because the perpendicular layers support each other.

Builders use plywood for floors, walls, roofs, and furniture because it's strong, relatively inexpensive, and comes in large, flat sheets that are easy to work with. When you see construction workers carrying big rectangular panels to build a house, they're often carrying plywood. The invention of plywood in the mid-1800s revolutionized construction, making it possible to cover large areas quickly and reliably. Today, plywood remains one of the most versatile materials in any workshop or construction site.