When you look at the edge of a corrugated box, you see three layers: two flat liner sheets with a wavy (corrugated) medium sandwiched between them. That wavy layer — called the "flute" — is what gives corrugated board its remarkable strength-to-weight ratio. But not all flutes are created equal.
What Is a Flute?
The flute is the arched layer of corrugated medium between the liners. Its wave-like structure creates a series of connected arches — one of the strongest structural shapes in engineering. This is why corrugated board can support significant weight while being made primarily of paper.
- Flute height: How tall each arch is
- Flute frequency: How many arches per foot of board
These two variables create distinct flute types, each with different performance characteristics.
The Main Flute Types
A-Flute - **Height:** ~3/16" (4.8mm) - **Flutes per foot:** ~33 - **Characteristics:** The original corrugated flute. Tallest arches provide excellent cushioning and stacking strength. Preferred for fragile items and when maximum protection is needed. - **Best for:** Fragile goods, heavy stacking requirements, cushion-sensitive products
B-Flute - **Height:** ~3/32" (2.4mm) - **Flutes per foot:** ~47 - **Characteristics:** Shorter, more densely packed flutes create a smoother surface for high-quality printing. Good crush resistance. Thinner profile saves space in shipping. - **Best for:** Retail displays, die-cut boxes, canned goods, printed packaging
C-Flute - **Height:** ~9/64" (3.6mm) - **Flutes per foot:** ~38 - **Characteristics:** The most widely used flute type in the world. Offers a balance between the cushioning of A-flute and the printability of B-flute. Good all-around performer. - **Best for:** Shipping boxes, general packaging, most commercial applications
E-Flute - **Height:** ~3/64" (1.2mm) - **Flutes per foot:** ~90 - **Characteristics:** Very thin profile with an extremely smooth surface. Excellent for high-resolution printing. Lighter weight than other flutes. Limited cushioning capacity. - **Best for:** Retail packaging, cosmetics boxes, pizza boxes, consumer electronics packaging
F-Flute - **Height:** ~1/32" (0.8mm) - **Flutes per foot:** ~128 - **Characteristics:** The thinnest common flute. Ultra-smooth printing surface. Often used as a sustainable replacement for folding carton (solid paperboard). - **Best for:** Premium retail packaging, fast food clamshells, small consumer goods
Double-Wall and Triple-Wall
For applications requiring greater strength, multiple flute layers are combined:
BC Double-Wall: Combines B-flute and C-flute layers with three liner sheets. Excellent strength with moderate thickness. Handles 50–80 lbs. Common in shipping heavy products.
AC Double-Wall: Combines A-flute and C-flute for maximum strength. Used in heavy industrial applications. Can handle 80–120 lbs.
Triple-Wall: Three flute layers (typically A-C-A or A-B-A) with four liner sheets. Extremely strong — can replace wooden crates in many applications. Handles 300+ lbs.
How Flute Type Affects Used Box Quality
Understanding flute types is especially relevant when buying used boxes:
- A and C-flute boxes tend to maintain their structural integrity well through multiple use cycles. The taller arches are more resilient to compression.
- B and E-flute boxes are more susceptible to crush damage in used applications. Look for Grade A stock if you need used thin-flute boxes.
- Double-wall boxes are the most durable used option. The dual flute layers provide redundancy — even if one layer is partially compressed, the other maintains the board's strength.
When you're uncertain about which flute type you need, start with C-flute. It's the most versatile option and the most commonly available in used inventory.