Heavy Duty Shipping Boxes (Double Wall, ECT-44 to ECT-51)
16x16x6 ECT-48 Double Wall Corrugated Boxes - Heavy Duty Kraft, Bundle of 15
PN: HD16166DW
16x16x16 ECT-71 Heavy-Duty Double Wall Boxes - 140# Capacity, Bundle of 15
PN: HD161616HDDW
16x16x16" ECT-48 Double Wall Corrugated Boxes - Heavy Duty, Bundle of 15
PN: HD161616DW
16x16x18 ECT-48 Double Wall Boxes - Heavy Duty Kraft Cartons, Bundle of 15
PN: HD161618DW
12x12x48 ECT-48 Double Wall Kraft Boxes - Heavy Duty Shipping Cartons, Bundle of 10
PN: HD121248DW
14x4x68 ECT-44 Kraft Side Loading Boxes - 10 Pack Bundle
PN: HD14468FOL
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Overview
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
| Grade | Construction | Typical contents limit | Replaces (burst-test class) |
|---|---|---|---|
| ECT-44 | Heavy single wall / light double wall | ~65 lb | 275# single wall |
| ECT-48 | Double wall | ~80–100 lb | 275# double wall |
| ECT-51 | Double wall, heavy | ~120 lb | 350# class |
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.
Buying path
Buy Heavy Duty Shipping Boxes (Double Wall, ECT-44 to ECT-51) by the specs that change the order
Use filters, product titles, and product pages to compare size, material, pack count, case quantity, and fit before ordering.
Use filters and product titles to narrow by the specs that affect fit.
Open the product page before ordering a case so you can check quantity, unit, and limits.
Save the SKU or product link for repeat purchasing and support questions.
For pallet, recurring, or mixed-SKU needs, send support the details before placing a large order.
What to check first
- Inside dimensions
- Board grade or strength rating
- Box style and closure
- Case or bundle quantity