The underlying layer of the floor In simple words

The underlying layer of the floor is a layer that distributes loads on the ground.

It is either a hard or soft material that is installed under the floor covering and above the floor base and performs the following functions:

1. Aligns the defects of the base;
2. Softens the floor covering, which is easier to walk on;
3. Protects against moisture penetration;
4. Provides proper sound insulation.

Foam, cork and rubber are common soft underlying materials. The solid materials of the underlying layer include plywood and hardboard.