ECT, BF and flute: corrugated strength explained for Indian buyers
ECT (edge crush) and BF (bursting factor) are lab strength numbers for corrugated board; flute letter (B, C, E) changes how the wall cushions versus stacks — for everyday Indian parcels, start with the right ply and a snug fit, then ask your supplier for ECT/BF only when you are writing a bulk or export spec.
Updated 11 Sept 2026 · PackWorks By Velun, Karnal
What buyers actually need to know
Indian catalogues rarely print a full lab sheet on every SKU. PackWorks labels board as 3-ply or 5-ply and publishes inner size — that is enough for most D2C and marketplace sellers. ECT and BF matter when a 3PL, exporter or purchase officer writes a purchase order that must match a previous vendor’s board.
ECT vs BF in plain language
Edge Crush Test (ECT) measures how hard you can squeeze the flute edge before it collapses — it predicts stacking strength on a pallet. Bursting Factor (BF) relates to how much pressure bursts the liner — it predicts puncture and rough handling. A high BF with a weak flute can still crush in a tall stack; a high ECT with thin liners can still puncture on a sharp corner.
| Spec | What it predicts | When to ask for it |
|---|---|---|
| ECT | Stacking / warehouse crush | Export, 3PL SLAs, tall pallet loads |
| BF / burst | Puncture and rough throw | Glass, metal edges, open tempos |
| Ply (3 / 5) | Wall count (flutes + liners) | Everyday e-commerce buy |
| Liner GSM | Stiffness and print face | Print jobs and heavy cubes |
Flute letters without the jargon
Flute is the wavy middle layer. B-flute is common on Indian e-commerce cartons — thinner profile, good puncture resistance, prints cleaner. C-flute is taller — more cushion, slightly thicker outer size. E-flute is fine and stiff — used on retail cartons and some mailers. Two flutes in a 5-ply board (often B+C) is why double-wall stacks harder than single-wall.
- Same ply, different flute → different crush and outer thickness
- Taller flute → more cushion, slightly worse print and a fatter outer for volumetric
- Finer flute → flatter print face, less air cushion
What to do on PackWorks
Pick 3-ply for parcels under about 5 kg that are not stacked high; pick 5-ply for heavy, stacked, monsoon or export loads. If a buyer’s PO demands a minimum ECT, tell us on the RFQ with your size and we will confirm board before you commit to a print run. Always drop-test a sample pack with your real product — a lab number does not replace a failed courier claim.