Shipping Box Strength & Durability: A Guide

Goods arriving at their destination, having been crushed in transit, are costly in more ways than one. It will frustrate the customer, necessitate the expense of resending a replacement product and ultimately affect a business’s reputation.

The key to a good shipping box is basically a mathematical formula. Strength and durability over weight. When it comes to the weight of a shipping box, particularly when shipping items overseas, every gram counts.

As experts in the field of mailing and shipping boxes, EB Packaging stocks only the finest quality boxes, robust, economical and lightweight. We understand how important it is for your products to arrive safely at their destination, for both your customers' satisfaction and your business reputation.

Cardboard vs Corrugated 

To the layperson, cardboard boxes and corrugated boxes are interchangeable terms. This is a misconception. Cardboard is generally made from pulp paper, and being less strong than corrugation, is less suited to mailing or carrying and more suitable for lightweight packaging.

Corrugated cardboard has several strength tests – the Mullen Test, which measures the amount of pressure a sheet can take when suspended horizontally in mid-air and the Edge Crush Test (ECT).

For mailing boxes, ECT is the most relevant as it shows whether a box is capable of holding the weight of its contents without crushing or bursting.

Below is an example of recommendations for content weight in relation to box ECT, and bursting strength. 

Minimum Bursting Test

Minimum ECT

Size Limit of box dimensions

Max weight of box and contents

125 

23

30

5-10 kg

250

44

85

50 kg

350

N/A

105

80 kg

Test weights in kg per sq.cm

Corrugated cardboard comes in a variety of strengths and the weight and type of paper used in its manufacture play a significant role in the strength of boxes made from it. The thickness of corrugated cardboard ranges from single-wall and double-wall through to triple-wall, able to hold 50 to 100kg plus weights. Single wall is made up of liner sheet, a layer of flute topped by another liner sheet. As the name suggests, the double wall consists of two layers of flute separated by a liner sheet.

Flutes for strength and resistance

Corrugated cardboard’s strength comes from the physics of weight distribution delivered by s-shaped paper or ‘flutes’ that lay between the cardboard liner sheets. Flute sizes are graded from A to F, with ‘A ‘Flute cardboard is generally about 5 mm thick and suited to protecting fragile items. ‘F’ flute being the thinnest, is suitable for packaging that requires stiffness. The concentration or distribution of flutes can dictate the strength of the cardboard with the denser the flutes translating to more robust boxes.

Above: example of EB Packaging’s 220 x 160 x 77mm A5 Regular Brown Mailing Box - single flute 

Above: example of EB Packaging’s 270 x 135 x 175mm Double Wall Heavy Duty Shipping Carton - flat

Which corrugated box do I need?

The weight, contents and use of the box will dictate the best option for your needs. Prior to purchasing boxes ask a few simple questions:

  • Is the product fragile?
  • Does the product bend?
  • How heavy are the contents?
  • Will the box need to accommodate a substantial amount of packing material?
  • Does the exterior need to be robust enough to prevent puncturing?

If the box needs to be printed and will only hold lightweight, non-fragile products, 32 ECT may suffice. The thinner cardboard can be easier to print on.

On the other hand, 44 ECT is sturdier, but the surface will be more undulating and therefore harder to print on.

Obviously, for fragile and valuable items, the ECT will be of significance and we would recommend our heavy duty mailing boxes with double wall corrugation.

If you run a business and are posting the same sized item regularly, why not drop us a line and let our expert team guide you to the best, most affordable option for your needs?

Talk to the Experts

EB Packaging stocks a wide range of packing boxes for every type of product. In fact, we have everything you need to protect your goods in transit including courier bags, packing materials, gift and coloured boxes for a personalised touch, protective packaging, bubble wrap and packing peanuts – we are literally a one-stop-shop for packaging!

If you run a business and are posting the same sized item regularly, why not drop us a line and let our expert team guide you to the best, most affordable option for your needs? Visit our wholesale page and save when you buy in bulk!

Shop online or email us at info@ebpackaging.com.au. EB Packaging offers friendly advice and service to make posting goods a smooth and rewarding experience, every time.