AC double wall: thickness, flutes per foot and strength

AC double wall pairs an A flute with a C flute, about 0.34 in thick in Packgent's nominal sum. It is the thickest common double wall, chosen for stacking strength and cushioning.

Key numbers

Construction	Double wall: two mediums, three liners
Plies	A flute + C flute
Nominal caliper	0.3438 in · 8.8 mm
OD minus ID, length and width	0.688 in
OD minus ID, depth	1.031 in
McKee strength vs C flute, same ECT	148%

Caliper is the sum of A flute (0.1875 in) and C flute (0.1563 in), computed by Packgent. Real board is slightly thinner after combining and converting.

Strength ratio = √(caliper ÷ C-flute caliper), from the McKee formula with ECT and perimeter held equal.

Trade-offs

Highest McKee estimate of the double walls at the same ECT
Bulky: outside dimensions grow fastest
Availability depends on plants running A flute

Typical uses

Tall, heavy stacks in storage
Large boxes that need cushioning from the wall

Estimated box compression at 10 sizes

Simplified McKee BCT, lbf, empty box, by inside size and ECT
Inside size, in	42 ECT	51 ECT	71 ECT	82 ECT
8 × 6 × 4	765	929	1,293	1,493
10 × 8 × 6	867	1,053	1,466	1,693
12 × 12 × 12	1,002	1,216	1,693	1,955
14 × 10 × 8	1,002	1,216	1,693	1,955
16 × 12 × 10	1,082	1,314	1,829	2,112
18 × 12 × 12	1,120	1,360	1,893	2,186
18 × 18 × 18	1,227	1,489	2,074	2,395
20 × 16 × 14	1,227	1,489	2,074	2,395
24 × 18 × 18	1,325	1,609	2,240	2,587
24 × 24 × 24	1,416	1,720	2,394	2,765

BCT ≈ 5.87 × ECT × √(caliper × perimeter), perimeter = 2(L + W) of the inside size. An estimate; confirm with ASTM D642. Grades shown are ECT values Packgent computes for this wall type, not a list of what mills sell.

Sources

Last reviewed 2026-10-27. See all sources and how Packgent computes.