Highly rated fiberglass tub cleaners include a homemade solution of white vinegar and baking soda and a paste of borax and lemon juice, according to SF Gate. These natural cleaning agents are safe and effective for fiberglass tubs, showers and hardware.
White vinegar is a powerful, non-toxic cleaning agent that disinfects fiberglass tubs and showers. Cleaning a tub with vinegar involves covering the fiberglass with baking soda, and misting white vinegar over it to form a paste. Vigorous scrubbing removes most dirt and soap scum. Extremely dirty fiberglass tubs benefit from scrubbing with borax and lemon juice, enhanced with a small amount of liquid soap or hydrogen peroxide if tenacious stains are present.