CD Vs. CDX Plywood

Plywood Grades

• The first of the two letters for a plywood panel grade are used to grade the front, or face side. For example, the face side might be used for the front of a cabinet or the top surface of a countertop. The second letter represents the grade for the back side. The back side is often less visible. You might only see the back side when you open a cabinet or if you look underneath a countertop.

C-Grade Plywood

• There are two “C” grades for plywood -- C and C-Plugged. C-grade plywood is allowed to have a set quantity and range of splits, small knots and overall blemishes. For example, a C-grade panel is allowed to have up to eight visible knots. A C-Plugged panel ranks higher, gradewise, and will have smaller knots, splits, cracks and imperfections. A C-grade is the lowest recommended grade to use for exterior applications, such as roofing and sheathing.

D-Grade Plywood

• Grade D plywood is allowed to have knotholes and imperfections up to three inches across the grain or cracks of the panels and up to 10 visible knots. Panels with a D-grade for the front are not recommended for exterior use. Grade D plywood is not moisture resistant and will swell and break down after extended exposure to water.

CD Plywood

• When a panel is labeled “CD,” it means that the front side has a C-grade and the back side has a D-grade. The plywood is formed from an odd number of plies, such as three, five or seven, glued and bonded together under heat and pressure to form one cohesive panel. Exterior CD-grade plywood is commonly used as a roof sheathing material. CD-grade interior plywood is used as a surface and as a substrate or base material for woodworking projects and for interior wall sheathing. In most instances, it is used when the surface will be painted or covered with another material, including drywall, particleboard or a higher grade of plywood, such as an A- or B-grade panel.

CDX Plywood

• CDX is the name used for plywood that has a C-grade front and a D-grade back. The letter “X” does not stand for a grading. The long name for CDX is “CD Exposure 1 Plywood.” The term “Exposure 1” indicates that the plies are glued together with exterior glue. However, although exterior glue is used to bond CDX plies, CDX plywood is not recommended for outdoor use, other than structural purposes.

CD and CDX Comparison

• CDX is more frequently used for temporary purposes, and CD is used for permanent applications. For example, builders will use CDX to construct forms for mixing and pouring concrete on a construction site and for temporary flooring. They lay CDX on the ground outdoors so that they have even footing while working, and they lay it down to use as temporary floor mats to prevent marring and damaging interior subfloor surfaces while working indoors. However, CD-grade plywood is used for permanent applications such as interior wall sheathing and exterior roof sheathing.