"Sub bed" is a phrase used to describe a layer of material that is placed beneath another surface. Some synonyms for "sub bed" include "base layer," "foundation," "substratum," "underlayment," and "support layer." These words accurately depict the function of a sub bed, which is to provide stability, support, and a flat surface for the layer or material placed above it. The use of synonyms is important because it allows for better communication and understanding of the specific materials and layers used in construction, landscaping, and other projects where a sub bed may be necessary.