In the process of piano manufacturing, the side (or outer rim) is typically added to the frame after the assembly of key internal structures such as the action, soundboard, and strings. However, in some models, like Steinway grand pianos, the side and frame are built simultaneously.

In grand pianos, several parts of the side are removable, such as the rear cover, front cover (hinged together), the cylinder (keyboard cover), and the fallboard. In upright pianos, the front area is generally closed with panels that include the cylinder and the fallboard. The top lid of upright pianos typically opens from front to back, although in some models, it is positioned on the left side. The backboard in upright pianos, when simply screwed in and not glued to the sides, can be easily removed.

The panels that make up pianos can be made from solid wood, plywood, or particleboard. Solid wood panels are often veneered on both sides to prevent warping. Particleboard, being heavier than other materials, contains a large amount of glue, making it denser. This material is often used for the lids of grand pianos, which are typically heavier. However, one issue with particleboard is that the screw holes can easily strip, so solid wood inserts are often used to reinforce it.

The side coverings are not only an aesthetic concern but also serve to prevent the wood from warping. After sanding the surface, the wood is treated with filler, sealant, stains, and several layers of finish to protect the piano from moisture. In pianos built in the United States, lacquer is the most common finish, while in Europe and Asia, polyester is generally preferred. Lacquer finishes tend to be satin or treated with steel wool, while polyester finishes are polished to achieve a high gloss. Each finish has its advantages and disadvantages: lacquer, although easy to apply and repair, is more susceptible to scratches and does not offer complete protection against water vapor. On the other hand, polyester, which is more scratch-resistant and seals the wood better, tends to be more fragile and can easily be damaged at low temperatures or due to the contraction and expansion of the wood.