C Flute Cardboard: What It Is and When to Use It

C flute is the most widely used corrugated cardboard in the world, accounting for roughly 80% of all corrugated packaging produced globally. With a thickness of approximately 4mm and 39–43 flutes per linear foot, it strikes the ideal balance between cushioning, stacking strength, and printability — making it the go-to choice for shipping boxes, retail packaging, and product displays alike.

What Is C Flute Cardboard?

C flute is a type of corrugated cardboard defined by the size and spacing of its inner fluted layer — the wavy, S-shaped medium sandwiched between two flat linerboards. The "C" designation refers to a specific flute profile standardized by the corrugated industry.

Here are the key physical specifications of C flute:

• Flute height: approximately 3.6–4.0mm
• Flutes per linear foot: 39–43
• Total board thickness (single wall): approximately 4mm (5/32 inch)
• Good compression and crush resistance
• Smooth outer surface suitable for high-quality printing

The fluted inner layer acts like a series of tiny arches, distributing weight and absorbing impact across the entire board surface. This structural design is why corrugated cardboard — and C flute in particular — performs so much better under load than solid paperboard of a similar weight.

C Flute vs. Other Flute Sizes

Understanding how C flute compares to other common profiles helps you choose the right board for your packaging needs. The most frequently encountered flute types are A, B, C, E, and F.

C flute sits between A and B in terms of thickness, but it inherits the best properties of both. It offers better stacking strength than A flute and superior cushioning compared to B flute, which is precisely why it dominates the general packaging market.

Key Advantages of C Flute Cardboard

Compression and Stacking Strength

C flute performs strongly in Edge Crush Test (ECT) ratings, a standard industry measure of how well corrugated board resists being crushed on its edge. A single-wall C flute board typically achieves an ECT rating of 32–44 lbs per linear inch, depending on the linerboard weight. This makes it well-suited for palletized shipments where boxes are stacked several layers high during transit and warehousing.

Cushioning and Impact Resistance

The relatively tall flute profile of C flute creates more air space within the board, which acts as a shock absorber. This is particularly valuable for electronics, glassware, and packaged food products that must endure rough handling during last-mile delivery. In drop tests, C flute consistently outperforms thinner profiles like B and E flute at protecting contents.

Printability and Surface Quality

Unlike A flute, which has a slightly irregular surface due to its taller arches, C flute provides a smooth, stable printing surface. It is compatible with both flexographic and offset lithographic printing, making it ideal for branded shipping boxes and retail-ready packaging where visual presentation matters.

Machinability and Versatility

C flute processes efficiently on standard box-making machinery. It scores, folds, and die-cuts cleanly without cracking, which makes it compatible with a wide range of box styles — from regular slotted containers (RSC) to full-overlap and five-panel folder designs. Its versatility reduces the need to stock multiple board types.

Common Applications of C Flute Cardboard

C flute is used across virtually every industry that ships physical goods. Some of the most typical applications include:

• E-commerce shipping boxes — the standard RSC box used by most online retailers is C flute single wall
• Food and beverage packaging — bulk cereals, canned goods, and bottled products often use C flute outer cases
• Electronics — appliances, laptops, and consumer electronics rely on C flute for both inner and outer packaging
• Furniture and home goods — flat-pack furniture manufacturers favor C flute for its stacking strength
• Retail display packaging — shelf-ready packaging and point-of-sale displays benefit from C flute's printability
• Industrial components — machine parts and automotive components are often shipped in heavy-duty C flute double-wall boxes

Single Wall vs. Double Wall C Flute

C flute is available in both single-wall and double-wall configurations, each suited to different load and protection requirements.

Single-wall C flute (one fluted layer between two liners) is the standard format and handles most shipping needs for goods under 30–40 lbs. It is lightweight, cost-effective, and easy to handle.

Double-wall C flute — or combinations like B/C or A/C — sandwich two fluted layers between three linerboards. This roughly doubles the stacking strength and is commonly used for heavy industrial goods, bulk quantities, or goods that require extra protection during long-haul freight. A B/C double-wall board typically achieves ECT ratings of 48–71 lbs per linear inch, far exceeding single-wall performance.

When C Flute May Not Be the Right Choice

Despite its widespread use, C flute is not always the optimal solution. Consider alternatives in the following scenarios:

• If you need very high-quality lithographic printing with fine detail, E or F flute provides a better printing surface due to their finer, denser flute pattern.
• For compact retail packaging where shelf space is a premium, E flute's thinner profile reduces box footprint without sacrificing much strength for light items.
• When packaging very heavy machinery or dense goods over 65 lbs, triple-wall boards or heavy-duty A flute combinations will outperform standard C flute.
• For high-volume die-cutting runs requiring very clean cut edges, B flute's flat crush resistance can be preferable.

How to Select the Right Linerboard Weight for C Flute

The performance of C flute cardboard depends not just on the flute profile but also on the weight of the linerboards that sandwich it. Linerboard is measured in pounds per 1,000 square feet (MSF) in the US, or grams per square meter (gsm) internationally.

Common linerboard configurations for C flute single-wall include:

• 23/23 lbs — light-duty, suitable for packaging under 20 lbs with minimal stacking
• 26/26 lbs — standard-duty, the most common configuration for general e-commerce shipping
• 33/33 lbs or 42/42 lbs — heavy-duty, used for heavier products or warehouse stacking requirements

For most standard business shipping needs, a 26/26 lb C flute single-wall box will be more than sufficient — and it is the configuration stocked by most corrugated box suppliers as their standard product.