The difference between composite and steel fence posts from Home Depot is that steel fence posts are made from steel while composite posts are made from recycled plastic. Specifically, composite posts are made from used plastic milk jugs, shopping bags and sawdust.
Home Depot offers square composite posts in 3.5 x 3.5 inch, 4 x 4 inch and 5 x 5 inch diameters, and in lengths of 64 inches, 96 inches and 12 feet. Home Depot also stocks a 5 x 5 inch x 8.5 foot I-beam profile fence line post for agricultural applications. Composite posts come in a variety of colors that imitate natural wood tones. Composite posts do not rust, rot, fade or conduct electricity, and they contain material that would otherwise end up in landfills.
Steel posts come in four varieties: round pipe posts, light-duty U-posts, heavy duty T-posts and rectangle-shaped posts. Steel posts are available in white, black, green and galvanized finishes. The rectangular posts are galvanized with vinyl coating. Steel post colors may be painted on or powder coated. All steel posts are between 1 3/8 inches and 3 1/8 inches in diameter. The longest steel post available is 10 feet. Steel posts are far less expensive than composites for the same length of post, but composites outlast steel posts.