We use CDX plywood to build the interior components of most of our furniture. We use a combination of CDX plywood and 2x4 studs. Plywood is a type of wood made of thin veneer sheets glued together. Plywood is know for its strong resistance to crack, breaking or twisting. Most of the plywood that we use is 5/8 inch plywood which is also referred to as 22/32 plywood. It is actually a little thinner than 5/8 but that is the closest nominal size. The 5/8 plywood that we use is typically 3 layers of wood and the grain alternates direction. The alternating grain is what really gives the plywood strength. There are different grades/classes of plywood which are represented by letters A, B, C and D. A is the most expensive and best quality, in terms of the number of knots on it. The less the number of knots, holes and repaired defects the more expensive the plywood.
C in CDX means one side of the plywood is grade C and the other is of grade D. 
This would matter if the wood was going to be visible for the finished product. Since our plywood is internal, we mostly care about the strength of the wood. X stands for exposure, which is the type of glue used to bind the layers of plywood together. The grading is not about the quality of the wood but more about the the appearance of the wood. CDX is strong and resistant to damage. This makes it the perfect wood to use when building the internal components of our furniture. Roof sheathing is one of the most common exterior uses of CDX. Usually, this plywood is passed through multiple processes that makes it strong and water-resistant. This makes CDX plywood a good choice of material as far as exterior applications are concerned. Besides, in cases when it absorbs water (since it is not waterproof), CDX will dry fast and lose the water over time and get back to its original size.
Many companies use particle board instead of plywood. Particle board can work for some uses, but if you have your choice between particle board and plywood, you always want to choose plywood. Plywood is stronger, lighter, and better resistant to moisture. Particle board breaks apart if it gets wet. Some of our more economical products use particle board, but we can always upgrade to plywood for any products. We always have it in stock in copious amounts.