What Are Shipping Containers Made Of? Corten Steel and Container Anatomy

Shipping containers are made primarily of Corten steel — a weathering steel alloy that forms a protective oxide layer instead of rusting through — welded into corrugated panels around a rigid steel frame. The floor is usually marine-grade plywood or bamboo over steel cross members, and the double doors seal with rubber gaskets and steel locking gear.

Corten steel: the material that makes it work

Corten, or weathering steel, contains small amounts of copper, chromium, and nickel. When the surface is scratched or exposed, it oxidizes into a dense patina that slows further corrosion — the opposite of ordinary steel, where rust keeps eating inward. Combined with marine-grade paint systems, it's why a box built to cross oceans can then sit in a field for decades.

The walls aren't flat for a reason. Corrugation — the repeating wave profile — dramatically stiffens thin sheet steel, the same way folding a sheet of paper lets it stand on edge. That's how container walls stay light enough to ship economically yet rigid enough to handle wind, racking, and rough handling.

The frame: posts, rails, and castings

The real skeleton is the welded frame: four corner posts, top and bottom rails, and a header over the doors. At each of the eight corners sits a corner casting, a thick cast-steel block with oval openings. Castings are where cranes lift, twist locks grab, and stacked loads transfer — the entire global container system is built around those eight blocks.

Floors, doors, and seals

Component	Typical material	What it does
Wall and roof panels	Corrugated Corten steel	Weather barrier and structural stiffness
Frame and corner posts	Heavy steel sections	Carries stacking and lifting loads
Corner castings	Cast steel	Lift points and twist-lock interface
Floor	Marine plywood or bamboo on steel cross members	Forklift-rated working surface
Doors	Steel panels, lock rods, rubber gaskets	Security and weathertight seal

The floor deserves attention when you buy. Treated marine plywood or bamboo panels sit on steel cross members and are rated for forklift traffic. On used containers, floors and door gaskets are the two components that show age first — check both, as our guide to how to buy a shipping container explains.

The door gear is a small machine in itself: vertical lock rods rotate cams into keepers at top and bottom, pulling the doors tight against continuous rubber gaskets. That's what makes a container "wind and watertight" — and why a bent lock rod or perished gasket matters more than a cosmetic dent.

Why the design lasts

Every part of the anatomy serves one goal: a sealed, stackable, liftable steel box with no load-bearing interior to get in your way. One-trip containers give you all of it in near-new condition; well-graded used units deliver the same engineering at lower cost for storage container duty.

The short version

Containers are built from corrugated Corten weathering steel on a welded frame, with cast-steel corner castings carrying every lifting and stacking load and a marine plywood or bamboo floor rated for forklifts. The lock-rod door gear and rubber gaskets keep the box wind and watertight. Get a free guaranteed-lowest-price quote on a new one-trip or used container — buy, rent, or rent-to-own — with delivery in 3–7 business days.