What do the letters mean?
The grading system for plywood is an easy puzzle to solve thanks to the simple A–D letter system used to indicate the quality of the panel. Plywood is graded per side, meaning that individual sides can be graded differently. The letters A, B, C and D typically refer to the veneer or face of the material.
PLYWOOD GRADES A & B
The highest quality—and most expensive—types of plywood are the A & B grades.
PLYWOOD GRADES C & D
The more economical types of plywood are the
C & D grades. This type of plywood grade is a good choice for projects where you will ultimately conceal the plywood panel with some other type of cover material.
THE LETTERS X
The letter “X” in CDX refers to the type of glue used in the factory to bond the plywood veneers. Some mistakenly think the “X” stands for “exterior”—which is not true. The letter “X” stands for exposure, which means the plywood is tough enough to withstand a little moisture—but for only a short time. Eventually, the panel must be covered by something more weather resistant—like bricks, siding or shingles.
CDX Plywood is used primarily by contractors to build exterior walls and roofs. CDX plywood has one side veneer grade “C” and one side veneer grade “D”. The two are bonded together with glue which can withstand a little moisture. The APA would recognize CDX Grade Plywood as C-D Exposure 1 plywood.
CDX DOES NOT AUTOMATICALLY MEAN PRESSURE-TREATED
Be careful not to confuse the words “outdoor,” “exterior,” and “pressure treated” to all mean the same thing. Pressure-treated plywood, which is saturated with chemicals to ward off mold, mildew, and insects, can survive outside for decades without paint or a protective finish.