The wood product known as chipboard is found in at least one application in most homes. It may be under the countertop laminate, under the flooring, in a bookcase, or in a door. No matter where it is, though, it is almost always covered up. Lower cost, availability and ease of tooling made chipboard the common building material it is today--but it isn't pretty.
Chipboard is made up of wood chips bound together with resin and pressed into a flat, rectangular shape. Pieces of wood that are too small, warped, or otherwise defective for use as lumber are splintered into small chips, and mixed with sawdust. A synthetic resin is added, usually urea formaldehyde, to hold the chips together and increase the strength and hardness of the finished product. The mixture is then heat-formed under pressure to create a smooth, rigid board.
Chipboard is available in three types--normal, medium, and high density, depending upon the amount of pressure used in the formation of the board. Normal density is relatively soft and easily worked, while high density is very hard and heavy. Chipboard is sold in 4-by-8 sheets, similar to plywood, and in a range of thicknesses, most commonly 5/8 inch and 3/4 inch.
Because chipboard is not considered a "beautiful" wood, the most common uses involve applications as a base or foundation, where the chipboard itself would ultimately be covered up. Most laminate countertops have a chipboard base, and many types of laminate flooring are installed over chipboard. Because of its low cost, chipboard is commonly used to build low-cost indoor furniture, especially the kind shipped in a flat-pack. High-density chipboard is rigid, durable, heavy, and even flame-retardant, making it a useful, yet inexpensive material.
Lower cost is the advantage most often cited about chipboard. While the initial purchase price of the board itself is only slightly lower than that of a comparable plywood, chipboard's smoother surface and texture allow builders to save money on tooling, while providing a ready-to-laminate surface. Because the wood fibers are not running uniformly down the length of the wood, chipboard is more resistant to warping, and will not splinter. Chipboard is available with a flame-retardant treatment, and high-density chipboard can have a water-resistant treatment.
Normal and medium-density chipboards are not water resistant. When it gets wet, all chipboard--except for high density--soaks up water due to capillary action from the wood fibers. This causes the wood fibers to swell, and the board will appear bumpy and rough. Because the board is made of many small chips, there are many more open fiber ends to soak in water. Because the fibers are in pieces instead of continuous as in solid wood, they don't work together to provide strength. Instead, water-logged fibers are weakened and the board breaks easily.