J&H American Enclosures' polymer concrete boxes are U.S.-manufactured, heavy-duty underground enclosures made from high-strength polymer concrete—composed of resin-bound aggregate—that deliver exceptional compressive strength and durability while being lighter than traditional concrete. Offered in a wide range of sizes (from compact 74 lb 11″×18″×18″ to massive 822 lb 36″×60″×36″ units), each box meets ANSI/SCTE Tier 22 load ratings with ± 1/8″ tolerances and is built in Alvarado, Texas under Build America, Buy America certification. Designed to withstand heavy soils, traffic loads up to 22,500 lb (with 33,750 lb test loads), and harsh environmental conditions, these boxes include covers and hardware that support safe access and long-term reliability. Ideal for utility vaults, splice points, and infrastructure projects, they offer a robust, precise, and domestically-sourced solution built to last.