Heavy Duty Shipping Boxes (Double Wall, ECT-44 to ECT-51)

Heavy duty shipping boxes for freight-class weight: every box here is double wall construction or rated ECT-44, ECT-48, or ECT-51 — the grades built for stacking strength and 65–120 lb contents that standard ECT-32 singlewall can't safely carry. Kraft corrugated, sold in bundle quantities with case pricing on the product page, shipped from 5 US regional warehouses.

How to choose: ECT-44 double wall for dense products up to ~65 lb per box; ECT-48 for ~80 lb or sharp-cornered industrial parts; ECT-51 for the heaviest palletized freight. If you're replacing a 275# burst-test spec, ECT-44+ double wall is the equivalent class. Not sure which grade? See the shipping box size chart or buying guides, or ask us for a spec match.

ECT grades at a glance

Typical industry guidance — the certificate stamp printed on each box governs. Every product page lists the exact grade.

Frequently asked questions

What does ECT mean on a box?
ECT is the Edge Crush Test rating — how much stacking force a corrugated box wall withstands, in pounds per inch of width. Higher ECT means more stacking strength: ECT-32 is standard shipping grade, while ECT-44 through ECT-51 are heavy-duty grades for dense or palletized loads.

What is the difference between single wall and double wall boxes?
Double wall boxes have two fluted corrugated layers between three liners instead of one, roughly doubling stacking strength and puncture resistance. They hold their shape under heavy contents and pallet stacking where single wall would bulge or crush.

What replaces a 275 lb test box?
As a rule of thumb, 275# burst-test single wall corresponds to about ECT-44, and 275# double wall to about ECT-48. When replacing a specified box, match the certificate stamp class rather than the nominal name.

Do heavy duty boxes cost more to ship?
They weigh slightly more per box, but carriers price mostly on total shipment weight and dimensions. Packrift shows live carrier-quoted freight at checkout from 5 US regional warehouses, so you see the real landed cost before ordering.

Updated August 1, 2026. Grades and counts refresh automatically as catalog stock changes.

Looking for sturdy shipping boxes that hold up under real freight? Every grade here is rated for exactly that — the ECT stamp tells you how sturdy, in numbers instead of adjectives.