This article demonstrates which stacking methods are used for different applications, where common errors occur, and which stacking method provides the greatest added value.
Lisa-Marie Bittner
Updated on June 2, 2026
→ In our 3D Tray Generator, you can also test, if you already have 3D data for your tray, which stacking method is best suited for your plastic tray.
If plastic trays and workpiece carriers can be stacked, this has advantages for production, storage and logistics.
If trays are to be stacked, this must be taken into account in the design, as additional space is required for stacking. A stackable tray is therefore usually slightly higher than non-stackable models. The tray height when loaded is then made up as follows, for example:
= 80 mm loaded Tray height
The total stacking height of this example results from the calculated tray height of 80 mm (loaded) and the stacking height of 10 mm per tray added with each tray. If certain outer carton dimensions are specified, it is possible to calculate how many trays fit into a packaging unit.
In the formary configurator, you can either adapt the tray to a specific carton or directly request a suitable carton for the specified stacking height.
When selecting the right stacking method for palletising, various points are decisive:
The required stacking of the tray depends primarily on the material thickness used. The stacking method often depends on whether the tray is used as a disposable or reusable product.
Can the next higher tray stack touch your components or rest on them, or are they touch-sensitive? If you are not allowed to stack over the components, but must leave a few millimetres of clearance to the next higher tray, then the stacking tray must be designed to be self-supporting - this requires robust palletising.
Simple stacking techniques, such as undercut stacking, are easier to implement than moving mould parts (a nap stacking) - and therefore shorten the lead time of your first samples.
Tip: With our 3D Tray Generator, a suitable stacking technique is recommended based on your component data.
The most commonly used stacking method in logistics is undercut stacking. An undercut is an inward-facing flange in the tray wall. These are not easy to mould during production, as they have to be removed from the thermoforming tool in the opposite direction to the demoulding direction.
Despite the more complex manufacturing process, undercut stacking offers several advantages:
The dimensioning of undercuts is based on the requirements of the transported components:
So which techniques are available and which should be used to avoid transport damage? That depends. We provide guide values based on your application or product. What you are primarily interested in when purchasing a tray is often the price - or the price-performance ratio. More complex technologies often have higher tool prices. We explain the background.
When palletizing stackable trays and workpiece carriers, there are various methods that are selected depending on weight, material thickness, and area of application. Below we present the four most important stacking techniques.
| Stacking method | Typical applications | Advantages | Disadvantages | Costs |
|---|---|---|---|---|
| Undercut stacking at the edge | Buckets, cups, small plastic containers | Cost-effective, can be integrated directly into the tool | Only suitable for light loads | Low |
| Undercut stacking in the wall | Single-use trays, small workpiece carriers | Fast production, inexpensive tools | Limited load capacity, problematic with heavy parts | Low–Medium |
| A/B stacking | Inlays, packaging trays, empty packaging | Very good separability, easy handling | Higher tooling costs due to two variants | Medium |
| Nub stacking with flap tool | Automation trays, robotics, heavy metal and automotive components | Highest stability, precise stacking, automation-capable | Complex tool, longer delivery time | High |
With smaller buckets and tubs, the undercut stacking does not need to be very pronounced due to the low weight. It can therefore be applied directly to the edge. This type of palletising is therefore particularly suitable for containers. Simple undercut stacking can be incorporated into the mould during design and is not cost-intensive.
Top undercut:
Undercut bottom:
We have already discussed what undercuts are. As products with a low weight only require a narrow stack, this can be incorporated into the mould without additional features (more on this later). This allows for low-cost moulds and fast production cycles. Just right for disposable trays.
The disadvantage, however, is that undercut stacking can naturally reach its limits with thin material. If the load is too heavy and the stacking does not support it, the undercut must either be maximised or the material thickness increased. If this does not help either, dimple stacking must be used (see point 4.).
Normal undercut stacking is usually used for transport and storage applications:
A/B stacking is a suitable solution for plastic inlays and packaging inserts.
Theoretically, two different thermoforming tools would be required for A/B stacking. In practice, however, alternatives can be used:
These approaches affect the price of A/B stacking, as the tooling effort is higher.
A/B stacking is particularly used for empty packaging, i.e., when empty trays are delivered to packaging lines for further processing. Advantages are:
If the stacking has to be very stable, dimple stacking is used for palletising. The stacking trays are supported and stacked by circumferential block segments. If trays contain heavy parts or if precise stacking tolerances of the vertical stack are required (e.g. in a palletiser of an automation system), this is the right technology.
The circumferential stacking cams are so strongly moulded that they could not be demoulded with a normal tool. For this reason, a flap tool is used:
This stacking method is more in the premium range, with more cost-intensive tooling construction and longer tool production times. Therefore, flap tool stackings are usually used in higher-value application areas, such as automation, where robot palletizing comes into play in addition to manual palletizing.
Are you having problems stacking your trays? We discuss the error patterns and their possible causes:
| Error pattern | Cause | Solution |
|---|---|---|
| Stack jammed |
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| Trays tilt and slip |
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| Stack tilts at an angle |
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The aim is to prevent jammed and wedged stacks and to achieve the most stable result possible.
The right stacking method helps to avoid transport damage by distributing the weight evenly and contributing to the stability of the load. The choice of the right palletizing technique should be tailored to the specific needs to optimize costs and minimize damage.
Would you like to benefit from this? Simply tell us the stacking height or the number of trays to be stacked when making your request.
The right stacking method for plastic trays is important because it prevents transport damage, makes storage and production processes more efficient, and reduces costs. Incorrect stacking can lead to unstable pallets, jammed trays, and damaged products.