Pouch Sorter

a winkler-technology Insights Article

Updated on 28.5.25

It doesn’t look at all like a sorter but everyone is using the term “Pouch Sorter” for overhead conveyor applications with hanging pouches. Let’s dig deeper into what a Pouch Sorter actually is and especially what the strengths and weaknesses of this concept are.

If we look at the underlying technology, the thing we see is a simple conveyor. An overhead conveyor with a little adapter or carrier to which a pouch or bag is attached. So what makes this a sorter?

It is a real sorter !

Well, actually unlike the so called sorters like the cross-belt, linear or shoe sorter the Pouch Sorter is actually sorting and not only diverting. A Pouch Sorter changes the sequences of the pouches in order to sort them. So let’s look at the conventional sorters first:

All of the ‘conventional’ sorters are either linear (“shoe sorter”) or circular (“cross belt-” / “split/push/tilt-tray-” sorter). The above picture shows that:

  • these sorters are actually only diverting. The sequence of the sorting goods is not changed. (“C” arrives after “A” at the same divert target)
    Theoretically a circular sorter could change the sequence, but this would require an extra loop, e.g. for “A” to arrive behind “C”. An extra loop means longer sorter occupancy, hence reduced performance. Therefore this is typically not done.
  • the total number of diverts is limited by the length of the sorter. Hence when dimensioning the length of the sorter the total number of potentially required additional targets in the future must be known.

In contrast the same schematic for the Pouch Sorter shows:

  • Sequence of sorting goods is changed to group goods together. All goods / items belonging to the same target are sequenced next to each other.
  • Therefore the number of sorting targets is not limited. Think of the output being one long sausage of sorted goods which can be cut in as many slices as required. Hence a sorter output of 1000 sorting goods can be sliced in 10 targets (of in average 100 pieces), in 100 targets (of in average 10 pieces), in 500 targets (of in average 2 pieces), in… you get the idea.
  • Even within a target (= “one slice of the sausage”) a desired sequence can be guaranteed, e.g. for optimized packing.

Of course the different “slices of the sausage” can be further diverted to different physical targets, e.g. several different packing stations. But logically the pouch sorter creates just one output line which uses a perfect sequence to group items belonging to the same target.

Matrix algorithm

Ok, but how does the Pouch Sorter change the sequence, hence does the sorting? There seems to be no specific sorting device in the system. A set of buffer lanes, diverts and merges is arranged in such a way that the hardware for the execution of the so called “matrix sort algorithm” is built.
(a good explanation of this algorithm can be found here: http://ijiset.com/vol2/v2s11/IJISET_V2_I11_69.pdf) .

The following picture shows a rather common set-up of Pouch Sorter implementations, the 8×3 or often also called 83 matrix. In this example the input flow is divided into 8 lanes. Of course this diverting into the 8 lanes is not done randomly, but follows the logic, the algorithm of the matrix sort method.

Such an 83 matrix

  • has a capacity of 512 elements (= sorting goods) per run
  • requires a buffer capacity of 64 elements (= pouches) per lane
  • typically takes 5 to 8 minutes to sort the 512 elements, hence to run through all three stages of the matrix sorter.

You do not need to dig into all the technology and algorithm details. The important thing to remember is:

A Pouch Sorter creates a perfect sequence of any given random input. With the common 83 set-up it takes 5 to 8 minutes to sort 512 elements.

Before moving on to actual use-cases and the pros and cons of the Pouch Sorter concept, let’s answer two frequently asked questions about the Pouch Sorter.

Performance of just 512 pouches in 6 minutes?

512 pouches in 6 minutes translates to 5 120 pouches sorted per hour. That’s not impressive compared to the performance of a typical crossbelt- or shoe-sorter. Well the 6 minutes relate to one full matrix sorter run across all the 3 stages of the 8³ implementation. As the stages are passed in a sequence it means that any finished sequence step (= set of 8 lanes) can already be filled with the pouches of the next sorting run. This leads to a typical real-life throughput of approx. 10 000 to 14 000 pouches / hour.

Why 8 to the power of 3 ?

Or why not 38, 44 or whatever? System design is aiming to achieve an optimum of several criteria. In this case the most important criteria are:

  • Operational ‘fit’ of the sorter capacity / of the sorting batch size:
    With something between 300 and 1000 items per sorter batch the requirements for upstream pre-sort is low (e.g. ensuring all orders within the batch are complete, no item is missing). Hence the sorter ‘fits’ to the operational environment.
  • Performance:
    For a sorter this translates into overall throughput (measured in items sorted / hour) and in duration (measured by how many minutes the sorting requires). As there is always a time gap between two sorter stages it is desirable to have fewer stages. Hence you will never see a 29 matrix instead of a 83 (equal batch size of 512).
  • Costs of the system:
    The most costly mechatronic elements of a Pouch Sorter are the diverts and merges. An 83 matrix requires 24 diverts and 24 merges for a batch size of 512 items. Having the above defined target of few stages in mind, a 23² matrix would combine short sorter runs with roughly the same capacity (529 pouches to be precise). But this would translate in 46 diverts and 46 merges, hence almost double the costs.

Therefore the most common specs of a pouch matrix sorter are 83 and 73 – the latter is preferred if the batch size of 343 items is sufficient.

Preferred Pouch Sorter applications

So far we concentrated on the sorting function of a Pouch System. The nature of the sorting function, the operation in batches, requires an integrated buffer. This is an important aspect as well as the fact that the technology is based on hanging pouches.

Let’s first understand the ‘hanging pouch’ thing before coming back to the integrated buffer. Instead of transporting a carton, a tote or a tray the items to be conveyed (and sorted) are placed in a pouch. The great advantage of this approach is that the pouch wraps around and adapts to the item. Also items with a distinct difference in length and width tend to lie in the pouch with the long edge normal to the conveying direction. In essence: the typical width of a loaded pouch for a mixed e-com SKU portfolio is around 70 to 100 mm.

This leads to two favorable consequences:

  1. Many items can be buffered within a relatively short conveyor length
  2. Conveyor throughput is determined by the speed and the distance of the conveyed units. With pouches this distance is very low, leading to typical throughputs of 10 000 to 15 000 pouches / hour.

High-performance, but limited

Sounds great, but the Pouch System also has major disadvantages:

  • Additional steps are required to load and unload a pouch – labor or machinery. Fortunately, several providers now offer robust and powerful solutions for automating this process. Nevertheless, this is of course an additional process, even if it takes place without human touch(es).
  • Pouches Sorters are limited in volume and weight. Hence the typical usage is for only one item per pouch with a max. weight of 2 to 4 kg.
  • Pouches are hanging from something like a hook. Hence the dynamics of the conveying operation translates into pouch movements – simply put: they swing around in and across the conveying direction. Especially in applications with largely varying item characteristics this leads to potentially unstable operations or the requirement for reduced dynamics, hence throughput loss.

Overview of Pouch Sorter properties

Let us summarize the main properties to deduce the preferred use cases of a Pouch Sorter:

  • Infinite number of sorting targets. Which supports a wave-less or a dynamic waves warehouse operation.
  • As the number of sorting targets and the target size (= order size) is just a parameter of the sorting algorithm (software) the performance is totally independent of the order structure.
  • Each pouch (= each item) is sorted individually.
  • Perfect sequences, also within a target / order is achieved without extra costs and without performance loss.
  • Sorting performance of 10 000 to 14 000 items / hour.
  • Sorting delay time of 5 to 8 minutes. (excluding pre-sort buffer!)
  • Limited to 2..4 kg / item with typical max. dimensions of 400x300x200 mm
  • Suitable also for cylindric, limp or odd-shaped products.
  • Sensitive to an SKU range with largely differing weight and size characteristics (reduced reliability or performance).
  • Extra effort for loading and unloading of pouches.

The perfect E-com machine

As already mentioned before, every matrix sorter requires a pre-sort buffer to assemble the pouches for the next sorter run. Together with the fact that the typical buffer conveyor length occupied by a loaded pouch is typically just 70..100 mm this enables the Pouch Sorter to seamlessly integrate individual return items.

The sweet spot of Pouch Sorters are E-com applications in sectors with substantial return rates and an SKU range with physical properties suitable for pouch conveyor technology. No surprise that the #1 industry sector for Pouch Sorters is apparel. Especially when the pouches are designed in such a way that also hanging garment can be hooked – which is the case for most pouch offerings on the market.

And Omni-channel?

At least in the glossy brochures Pouch Sorters are often also marketed as being perfect for Omni-channel. Which sounds logical for a sorter technology having a performance independent of order structures. However one should not forget the price to pay for using a Pouch Sorter: the loading and unloading of the pouches. In many applications it simply does not make sense to put for example 10 identical items into individually pouches if they are for the same target, e.g. the same store replenishment.

Also is does not make sense to have one-liners (orders with just one SKU) to go through a Pouch Sorter. Actually many real life Pouch Sorter layouts show a route outright bypassing the Pouch Sorter for one-liners.

Hence it depends on the specifics of the omni-channel demand whether a Pouch Sorter is the right solution. If for example shops require the replenishment to be sorted (e.g. by color or size) than the Pouch Sorter is unbeatable.

Brown field

The core technology of a Pouch Sorter is an overhead conveyor. Hence the bulk of the system can be installed under the ceiling, leaving empty operation and storage space underneath. This makes the Pouch Sorter a good tool for upgrades or modifications of existing warehouses and operations.

Summary

This insight article tried to provide you with in-depth information about the concept, the technology and the applications of Pouch Sorters. It is an interesting solution especially for E-com applications with substantial return rates. But it is important to understand the special characteristics and limitations of the Pouch Sorter technology.

Please let me know whether the objective is achieved, whether you are missing something or if you disagree with any statement.