It's marine grade and used to make boats. Each 4’ x 8’ sheet of plywood has waterproof glue and is without knot gaps, or air pockets in the layers.
Soft and hard wood has a tendency to be brittle and snap while plywood bends slightly and is more forgiving, so it works better as seat and back rest pieces.
Sanding the edges and giving each piece a coat of primer, before assembly, creates a chair that survives the elements. As with any outdoor furniture, it should get a fresh coat of paint every 3-5 years.
We use stainless steel (SS) carriage bolts, nuts and screws. SS is highly resistant to corrosion which makes it the best choice for outdoor furniture.
With stainless steel, the addition of nitrogen also improves resistance to pitting corrosion and increases mechanical strength.
We use 2" long SS screws to fasten all boards as the longer length provides for increased strength between connections and less flexing of the joint.
Spraying paint and primer allows the crevices between boards to receive a continuous thickness of material.
We spray primer onto each board before assembly to make sure that every piece is fully guarded against the elements.