Understanding Shipping Box Strength

Understanding Shipping Box Strength

Corrugated shipping boxes help keep your products safe and secure during transit. But did you know there are different types of corrugation and shipping box strength? At first, you might think that opting for the strongest corrugated box is the best choice, but it’s much more nuanced than that.

Stronger boxes are heavier and more expensive to ship. They also use more materials, making them the less sustainable choice. When stocking up on shipping boxes, you must consider the protection level your products need and find that sweet spot between protection and practicality.

As packaging experts, we know the ins and outs of shipping box strength and how to choose the perfect box for your products. Here’s our guide.

What are corrugated boxes?

Corrugated boxes are made up of layers of material to add strength to the packaging. The difference between cardboard boxes and corrugated boxes is that cardboard is typically made of a single sheet of material, while corrugated boxes consist of two sheets of cardboard with fluting in between. Cardboard boxes usually aren’t suitable for shipping; the thick paper protects items as internal packaging within a corrugated box.

Corrugated boxes come in various strengths, depending on the weight, fragility, and size of the products they carry.

How is corrugated box strength measured?

The strength of the shipping box sheet is described with a number and letter (e.g., 32B or 32ECT B). The number notes the Edge Crush Test (ECT) rating, which explains how much weight a single sheet can withstand if standing on its edge. The letter describes the tightness of the waves of the corrugate, otherwise known as the fluting. Let’s take a look at what both of these mean.

What is an edge crush test (ECT)?

The number in a box strength measurement refers to the ECT. It tells you how much weight a corrugated sheet can withstand when standing on its edge in a lab setting. For example, a 23A corrugated sheet can withstand 23 pounds of pressure, as can 23B, 23C, and 23E.

ECT determines whether a box is strong enough for its contents. Heavier products will need boxes with a higher ECT. But ECT isn’t the only thing you should consider when deciding box strength. The size and type of box you choose will also play a part. For example, a 32C box can carry more weight than a 32E box because it’s thicker.

Check out this reference from UPS outlining its recommendations for the minimum ECT for different box contents. UPS does not address 23B, so we have added our guidelines based on our experience.

*EcoEnclose recommendations; not provided by UPS.

What are flutes?

Flutes are the s-shaped, wavy paper between the linerboard of a corrugated sheet. It gives corrugated boxes their strength and resistance to bending and pressure. Flutes vary by their height and how tightly or loosely they are waved.

Below are standard flute sizes from thickest to thinnest.

• A Flute: 36 flutes per foot and 1/4" thick. While it works great for shock absorption, strength, and cushioning, it exceeds the needs of small carrier shipping. Not offered by EcoEnclose.

• C Flute: 39 - 43 flutes per foot and 11/64” thick. This is the go-to flute for standard box styles (RSCs and FPFs).

• B Flute: 42 - 50 flutes per foot and 1/8" thick. It’s designed to resist crushing and is good for folding, making it an excellent selection for TL and LM boxes.

• E Flute: 94 flutes per foot and 1/16” thick. The thinnest of the shipping-appropriate flutes, it makes an excellent printing surface and has a nice overall presentation.

• F Flute: 125 flutes per foot and 1/32” thick. It’s inappropriate for shipping or eCommerce, but it can be interesting for certain primary packaging applications. Not offered by EcoEnclose.

For added strength, corrugated sheets can also be double- or triple-wall. eCommerce shipping boxes are generally made with single-wall B, C, or E flutes, all striking an appropriate balance of strength and lightness.

Why shipping box strength is important

Cardboard strength ratings are essential to fully understanding the type of box you need. You can easily order your packaging once you know the specs of your corrugated box.

In terms of optics, choosing the proper shipping box strength will not only protect your items but also show your customers that you care. A high-quality box can often denote high-quality products and services to your customers. However, respecting your customers by keeping shipping costs low is essential. Thicker, heavier boxes might portray high quality, but they’ll cost more to ship. The shipping box strength you choose must protect your products, display quality, and minimize costs; it’s a delicate balance that can sometimes be difficult to find.

If you’re having trouble determining which shipping box strength measurements you need, contact us or order free samples to see which packaging suits your eCommerce business.

Learn more: The Ultimate Guide to Custom Shipping Boxes

Which corrugated box should I use?

When deciding which shipping box durability is best for your business and products, there are a few things to consider. You’ll need to consider box style, cost efficiency, and more to determine which custom shipping box best fits your brand.

Box style

For a presentation-style box (such as a Tab Locking Box or Literature Mailer), you will probably want to select a board that’s easy to fold, such as a B or E flute. While we make presentation boxes with thicker material, folding and creasing may be a little more cumbersome. We typically suggest 32 ECT C or 44 ECT for RSC (regular slotted container) boxes, depending on the weight of the product shipped. We can make most custom shipping boxes from most boards, but you should probably order a sample first.

Protecting your product

You’ll need something a little sturdier if you're shipping fragile items. When determining which box will best support your product, consider the following.

• Can your product be bent?
• Is the product heavy, and could it potentially break through the box?
• Will it need extra padding during transit?
• Does it need protection from punctures or other potential hazards?

Answering these questions will help you narrow down your packaging offerings.

Learn more: How to Package Fragile Items

Printing

If the aesthetics of the box are essential to your brand, consider tighter fluting. Some corrugated sheets, especially 32 ECT E, are thinner and sleeker, resulting in more successful printing. Conversely, the 44 ECT has fewer flutes that are twice as wide and create small ridges on the printing surface. Such ridges make it difficult to get an even print finish.

Cost efficiency

Consider the box cost, the inbound shipping (to your fulfillment location), and the outbound shipping (to your customer). Stronger board material usually has more cardboard material per square inch. This is going to cost more.

Ordering samples

It’s one thing to understand corrugated box strength in theory and another to see it in action. Before you choose your shipping boxes, order samples with a few different strengths. This way, you can see and feel it in person to gauge whether it offers the protection you want.

Are you feeling some decision fatigue? We’re here to help! Contact our support team and we’ll recommend which corrugated boxes will work best with your products.

EcoEnclose's Corrugated Sheet Strengths

EcoEnclose offers five different corrugated sheet options: 23ECT B Flute, 32ECT B Flute, 32ECT C Flute, 32ECT E Flute, and 44ECT C Flute. These strengths satisfy nearly all non-industrial shipping needs and are the most cost-effective options to meet said needs. As you consider your options, here is helpful information to determine the best sheet type for your box. Note these are EcoEnclose recommendations and are not provided by UPS.

23 ECT B Flute

• Recommended Box Style - LM, TL, OPF, Tray
• Definition - Economy: 1/8" thick. Our lightest weight and least expensive board that uses minimal source material. More subject to crushing as it is not as strong or as stiff as other options.
• Use If - You ship items that collectively weigh less than 5lbs, want to minimize costs or want a basic print on the outside of the box.
• Avoid If - You ship heavy items (>15lbs), have a large box (greater than 32 inches of L + W + H), and want to print on the inside of the box.

32 ECT B Flute

• Recommended Box Style - RSC, LM, TL, FPF, OPF
• Definition - Standard: 1/8" thick. Its higher ECT rating gives it more strength and rigidity than 23B and provides more cushion and shock resistance than 32E.
• Use If - You ship items that collectively weigh between 15lbs and 25lbs.

32 ECT C Flute

• Recommended Box Style - Large LM, Large TL, RSC, FPF, OPF, Tray
• Definition - Strength & Cushion: 11/64” thick. One of our two thickest options, providing even more cushioning.
• Use If - You ship items that collectively weigh 15-25lbs or have a larger tab locking box or literature mailer greater than 30 inches in L+W+H.
• Avoid If - You ship very light or small materials. B flute can be 15-20% cheaper than C Flute.

32 ECT E Flute

• Recommended Box Style - LM, TL
• Definition - Design: 1/16” thick. Thinner and more aesthetically pleasing than 23B and 32B. Same ECT rating as 32B, but is more subject to bowing and offers less cushioning.
• Use If - You ship items that collectively weigh 15-25 lbs. You want a very clean design, an excellent printing finish or to print on the inside of the box. Ideal for limited storage space because the material is thinner than B or C flute.
• Avoid If - You ship very light or small materials. Raw material on 23 ECT can cost 15-20% less than that of 32 ECT.

44 ECT C Flute

• Recommended Box Style - RSC, FPF
• Definition - High Strength: 11/64” thick. Our thickest option is heavy-duty and our most expensive board.
• Use If - You ship items that collectively weigh up to 40lbs or you have a high-value product that needs the heavy-duty crush protection.
• Avoid If - You ship very light or small materials. Raw material on 44 ECT can cost 40-50% more than that of 32 ECT.

Our three most popular shipping box strengths are 32E, 32B, and 23B. Notice the differences in thickness and the faint lines in 23B.

Where to buy corrugated boxes

You can buy them right here! Ordering custom shipping boxes is simple. Select your style, dimensions, strength, and branding, and we'll handle the rest. For branded orders, we’ll create proof of your artwork before production to ensure your vision is captured in a beautifully finished product.

Get started: Order custom shipping boxes here.