A bed foundation includes a frame and one or more panels positioned on top of the frame to define an upper surface of the bed foundation for supporting a mattress. The frame includes a plurality of rails which, when assembled together, at least partially define the frame. The plurality of rails are comprised of a thermoplastic foam that is lighter than wood or other similarly- or heavier-weighted materials commonly utilized in the construction of bed foundations, thereby facilitating easier shipping, lifting, carrying, and assembly of the bed foundation. The one or more panels can also be comprised of thermoplastic foam. The frame can further include a plurality of brackets to interconnect select rails of the frame. A kit for a bed foundation and a method of assembling a bed foundation are also provided.