A corrugated specification needs to distinguish construction, board properties and finished-box performance. “32 ECT C-flute” describes a strength value and flute family. It does not, by itself, establish how much a particular packed box can carry in storage.
1. Wall Construction Types
| Construction | Linerboard sheets | Fluted mediums | What to confirm |
|---|---|---|---|
| Single face | 1 | 1 | Intended wrapping, lining or other supported use |
| Single wall | 2 | 1 | Finished caliper, flute direction and board grade |
| Double wall | 3 | 2 | Both flute profiles and combined-board test values |
| Triple wall | 4 | 3 | Combined-board and finished-container requirements |
Scroll to compare all columns.
These are construction definitions from the Fibre Box Association. A larger number of walls is not a substitute for a performance specification.
2. Flute Profiles: Use the Supplier’s Finished Caliper
Flute letters are designations, not a sequence from thinnest to thickest. A and C are relatively large profiles; B is smaller; E and F are small-flute options. Actual geometry varies between manufacturers, even within one letter designation.
| Specification question | Why it matters |
|---|---|
| Which flute profile or combination? | Identifies the general construction |
| What is the finished caliper and tolerance? | Supports fit, outside dimensions and preliminary compression calculations |
| What direction do the flutes run in the erected box? | Establishes the intended load direction |
| What converting damage is acceptable? | Crushing during printing or die-cutting can change the finished board |
| Are measurements on incoming sheets or converted boxes? | Those are different sampling locations and may produce different results |
Scroll to compare all columns.
Avoid treating a nominal flute thickness as an exact material input. In particular, 1/4 inch is 6.35 mm, not 4.8 mm. For dimensional calculations, use a measured value or a clearly identified supplier nominal value with its tolerance.
3. Strength Specifications: Burst vs. ECT
ECT measures edgewise compressive resistance of a board specimen. 32 ECT conventionally means 32 lbf/in, approximately 5.60 kN/m. 44 ECT is approximately 7.71 kN/m. Identify the test method because specimen preparation and restraint are part of the measurement. TAPPI T 811 is one short-column ECT method.
Burst strength measures the hydraulic pressure at rupture under a diaphragm test. A 200 psi designation is a pressure value, not a 200 lb load allowance and not a direct measurement of sharp-object puncture resistance. TAPPI T 810 om-22 describes the burst measurement.
You can specify ECT, burst, or both when the application requires them. They answer different questions and cannot be converted into one another by a universal formula. Two boards with the same ECT may have different burst results, calipers and bending stiffnesses.
4. Read the Box Manufacturer’s Certificate Carefully
A Box Manufacturer’s Certificate can identify the relevant construction, board strength and size/weight limits. Read the complete certificate against the applicable carrier rules. A table pairing “32 ECT” with “200 psi” does not prove that the two boards are technically interchangeable.
Similarly, a certificate’s gross-weight limit is not the allowable top load for a stacked box. The current ASTM D5639/D5639M-25 performance-selection practice distinguishes material/certificate requirements from the performance needed across the distribution and storage journey.
5. Paper Weights: Identify the Basis
Basis weight is mass per unit area, often reported as g/m² or lb per 1,000 ft² for containerboard. It is not density or caliper. A liner/medium/liner recipe lists the components, but does not guarantee a particular combined-board ECT.
To compare quotations, ask whether the supplier is holding the paper recipe, measured board properties or finished-box performance constant. Those are different purchasing arrangements. Record which substitutions require requalification.
6. A Practical Specification Example
A preliminary request for quotation could read:
FEFCO 0201 shipping case; inside dimensions and tolerances per drawing; single-wall C-flute; minimum 32 lbf/in ECT using the agreed method; finished caliper and tolerance to be supplied; closure, print and joint per drawing; packed-box compression and distribution acceptance criteria to be agreed before production.
This is an example of specification structure, not a recommendation that 32 ECT suits a particular product. Add the intended gross mass, storage exposure, pallet support and stacking requirement before the supplier selects the final board.
Use Box Strength to compare preliminary combinations, then test the converted construction. The compression testing guide explains why a board value and a finished-box result are separate evidence.