Frames are what support the hot tub shell in portable spas. The frame also provides a structure to attach the hot tub equipment too. Things like heaters, pumps, control boxes, and ozone generators are components that typically get fastened to the frame of the hot tub. Frames are usually made from one of three different types of materials (metal, plastic, and wood). The first is metal. Although you would think metal would be a great choice, in reality, it is not. Because the environment of a hot tub is constantly humid and moist it can cause rusting of the metal frames. The second frame option is PVC or plastic pillars. PVC is better than metal because it won’t rust, however, it isn’t very strong and over time the constant, deadweight of the filled hot tub can cause the PVC to crack or fail. The third and most widely accepted frame material is treated wood. The word “treated” is very important as it will last substantially longer than an untreated wood frame. Many manufacturers use untreated wood to reduce manufacturing costs or they will use some hybrid where the base frame pieces (bottom) are made of treated wood and the upper frame and vertical supports are made from untreated wood. Our recommendation would be to get a fully treated wood frame that is 2”x3” thickness or greater. Another recommendation would be to find a manufacturer who does a unitized frame. A unitized frame is one that has the upper horizontal frame embedded into the fiberglass . Basically, when the hot tub shell goes thru the fiberglass stage the horizontal supports are laid onto the top rail of the shell and sprayed with fiberglass until they are completely covered. Once the fiberglass cures then other pieces of the frame (vertical supports) are screwed directly to the fiberglass covered horizontal supports.