Mixed palletizing is the job of stacking cases of different products onto one pallet so a single load can serve one store, one customer or one delivery drop. Done well, it saves trailer space and handling at the other end; done badly, it produces leaning, crushed loads that get refused on arrival. (The UK spelling is “palletising”, which we use from here on except where we’re naming the search term.) This guide covers what mixed pallets are, manual versus robotic mixed case palletizing, the order cases should go on, what keeps a load stable, and how a warehouse management system plans and tracks every case on the pallet.
What is mixed palletizing?
A mixed pallet carries more than one SKU. The trade often calls it a “rainbow pallet”, because a stack of different cartons in different printed boxes looks like stripes of colour. The opposite is a single-SKU or homogeneous pallet, where every case is identical and the stacking pattern can be repeated layer after layer.
Mixed pallets exist because customers rarely want a full pallet of one thing. A convenience store wants a few cases of crisps, some soft drinks and a box of cleaning products in the same delivery. A wholesaler’s trade customer orders twenty lines, three cases each. So the warehouse picks cases from many locations and builds them into one load. Dematic’s white paper on automated mixed case palletizing describes the work as three stages: breaking down full pallets into cases, buffering and sequencing those cases, then building the mixed pallet.
The reason it’s hard is geometry. Every case has a different footprint, height, weight and crush strength, so there’s no fixed pattern to follow. Researchers writing in the journal Sustainability treat mixed palletizing for smart warehouses as an optimisation problem whose aim is high load efficiency through good use of space. Photoneo puts it more plainly in its write-up on mixed-case palletizing with Jacobi Robotics: it’s a three-dimensional puzzle that has to be solved in real time, case by case.
It’s also physically hard work. Building pallets by hand means repeated lifting, twisting and reaching to the back of the base, which is exactly the kind of task the HSE’s guidance on manual handling at work asks employers to assess and reduce.
Where you’ll see mixed pallets
- Retail store replenishment: one pallet per store, often built to match the store’s layout so shelf-fillers can work aisle by aisle.
- Wholesale and trade distribution: many lines per order, low quantities per line.
- Pallet networks: part loads consolidated onto one base for overnight trunking through a hub.
- Cross-docking: inbound full pallets broken down and rebuilt as mixed outbound pallets without going into storage.
- Re-palletising in storage: part pallets combined onto one base to recover rack space, which creates a mixed pallet whether you planned one or not.
Manual vs robotic mixed case palletizing
Most UK warehouses still build mixed pallets by hand: a picker walks a route with a pallet truck and stacks cases as they’re picked. Robotic mixed case palletizing takes the stacking away from people, and it’s moved fast in the last few years. Here’s how the main approaches compare.
| Approach | How the pallet gets built | Stacking decisions made by | Best suited to |
|---|---|---|---|
| Manual pick-to-pallet | Picker stacks cases on the pallet truck while walking the pick route | The picker’s judgement | Low to medium volumes, wide product ranges, most 3PLs |
| Manual build at a staging area | Cases picked to totes or a conveyor, then stacked by a dedicated builder | A trained pallet builder | Sites where pick order and stack order can’t match |
| Robotic with sequencing | Cases buffered, released in a calculated order, stacked by a robot | Palletising software | High-volume DCs with storage and conveyor already automated |
| Robotic without sequencing (“on-the-fly”) | Robot uses vision to place cases as they arrive in random order | AI planning in the robot cell | Operations that can’t control the order cases arrive in |
Read the table as a spectrum of who decides where each case goes. In a manual operation, that decision sits with the person holding the case, which is why training and simple stacking rules matter so much. In a robotic cell, the decision moves into software.
The robotic market splits on one question: do you sequence the cases first, or not? WSR Solutions, which builds both manual and automatic mixed palletising systems, describes sequencing as putting products in the right order to get more flexibility and better stability. Others go the other way: Progressive Robotics markets on-the-fly mixed palletising that builds stable pallets from random product flows with no sequencing step. And Smart Robotics describes automated mixed case palletizing as robots using AI, sensors and vision to work out a stable, space-efficient pattern for each load.
When does automation make sense?
Robotic cells pay back where volumes are high, case formats are reasonably consistent and the same work happens every shift. They struggle with soft packaging, open trays and very irregular items. For a typical UK 3PL with dozens of clients and constantly changing products, the honest answer is that manual building with good rules and a good system is still the right choice for most of the floor. If you’re weighing it up, ask any vendor which of your actual case types their gripper can’t handle, and get a written go-live date rather than a range.
Build sequencing: the order cases go on
Whether a person or a robot is stacking, the order cases reach the pallet decides how stable the result is. The working rules are old and simple:
- Heavy and strong at the bottom: drinks, tins and dense cartons form the base. Light, crushable cases go on top.
- Big footprints first: large, square cases build a flat, even layer. Small or odd-shaped cases fill gaps higher up.
- Liquids never above dry goods: a split bottle ruins everything beneath it.
- Keep families together: if the customer unloads by category or store aisle, group those cases so they come off together.
- Last drop on first: on a multi-drop route, the pallet for the final stop goes deepest in the trailer, and on a shared pallet the last customer’s cases go on first.
The problem in a manual warehouse is that the pick route and the stacking order rarely agree. Walk sequence is set by where products sit in the racking, not by how heavy they are. If the crisps live near the start of the route and the bottled water near the end, the picker either builds an upside-down pallet or keeps lifting cases off and putting them back on. Fixing that is a slotting decision: put heavy, robust products early in the walk sequence so the natural pick order is also a sensible stack order.
Load order matters too. Mathew Buttar, Head of Solutions at Clarus, makes the point about picking against the transport plan: if a WMS knows nothing about which loads leave first, a team can pick the first twenty orders and stage them at the front, only to find they’re the last twenty due out. When the TMS sends load references and priority numbers back to the WMS, the warehouse can release work in departure order, so pallets get built and staged in the order the trucks need them.
Load stability: what makes a mixed pallet safe
A stable mixed pallet does three things: it stays within the footprint of the base, it doesn’t lean, and it holds together through handling, transport and unloading. The HSE’s warehousing guide, HSG76 Warehousing and storage, is the UK reference point for safe stacking and handling more generally.
The checks that matter
- No overhang: cases hanging over the edge of the base get crushed by forks, other pallets and trailer walls.
- Flat layers: build each layer to an even height before starting the next. Gaps and steps are where a stack starts to lean.
- Interlock where you can: turning cases between layers ties the load together. Columns are stronger for vertical crush but weaker against sideways movement.
- Height for the destination: check the maximum height for the vehicle, the racking it may go into, and the network or customer that receives it.
- Wrap from the base up: stretch wrap needs to lock the bottom layer to the pallet itself, not just bind the cases together. Corner boards help tall or light loads.
- Inspect the base: a damaged pallet goes no further until it’s restacked.
Poor stacking doesn’t always fail straight away. A badly built load can look fine leaving the pick face, then settle and lean over hours in racking or in a trailer. Mathew Buttar has seen the knock-on effect in racking, where a pallet that’s incorrectly stacked compounds over time until it leans out of the bay and falls onto the pallet beneath. That’s why part pallets returned to stock after a mixed pick deserve the same care as outbound loads.
How a WMS plans and tracks mixed palletizing
A warehouse management system isn’t a load-building algorithm. Robotic palletising software works out the 3D pattern; in a manual operation that stays with the builder. What the WMS does is make sure the right cases reach the pallet, records exactly what’s on it, and stops the wrong load leaving the building.
Give every pallet an identity
The foundation is a licence plate number (LPN): a unique barcode on each pallet that the system links to its contents. For outbound logistics units, the GS1 standard is the Serial Shipping Container Code (SSCC). In Clarus WMS these pallet IDs are called storage unit references, and Clarus recommends an 18-digit reference so the handheld scan flow stays GS1-compliant. The system won’t allow a duplicate reference for stock that’s live, but it will accept the same reference back once that pallet has been fully dispatched, so you can follow something that went out and came back. You can see how this works on the pallet and LPN tracking sida.
Build the pallet against the order, scan by scan
On a mixed pick, the handheld walks the operator through each line: go to this location, scan it, scan the pallet, scan the product, confirm the quantity. Clarus is task-driven at line level, so every pick line is a separate instruction, and a wrong location scan gets a red message showing where the operator should be standing. The handhållna arbetsflöden can be configured to the way each client builds loads, including plockning straight onto a pallet that’s been given its own reference.
This is where the labour saving shows up. Without scan validation, someone has to check every mixed pallet by eye before it’s wrapped. As Mathew Buttar puts it, with a paper pick list “they bring the pallet to you before they wrap it. You run around that pallet and check what they picked is what it says on the pick list… So, it’s taken two people’s worth of labour to ensure that the pick that was done was correct.”
He’s equally clear about the limit. Scanning confirms the location, the pallet and the product barcode, but an operator can still scan correctly and then lift a box from the pallet next door. A WMS reduces mixed-pallet errors; it doesn’t remove them, and nobody should claim it does. Spot checks on the wrapped load still have a place.
Receive mixed pallets properly too
Mixed pallets arrive as well as leave. When an inbound pallet carries standard GS1 labels, the scanner can read the article number, batch and quantity from the barcodes already on it, so the receipt captures what’s actually on the pallet rather than a guess. Our guide to the warehouse goods-in procedure covers receiving in more detail.
Tell the next party what’s coming
Once a pallet is complete, an automation can send an advance shipping notice to the receiver as the pick list closes, built purely from the scans. If the receiving site uses SSCC labels too, they can accept the whole pallet and its contents with one scan. For wider context on despatch, see our warehouse dispatch process guide, and for carrier booking, our overview of programvara för frakthantering.
Mixed pallets on UK pallet networks
The UK pallet networks run on mixed freight. Members collect pallets locally, trunk them overnight to a central hub, swap them onto vehicles for the destination region, and deliver the next day. A single pallet often carries several lines for one consignee, so the stacking rules above apply in full, and the networks are strict about it because a collapsed pallet at the hub delays everything behind it.
Each network publishes its own pallet types, with bands for weight and height, so the right answer for your load depends on which network your member belongs to. Check the current spec with your member depot rather than relying on a figure you remember. The practical rules are the same everywhere: one consignment per pallet unless agreed otherwise, a stable wrapped load within the footprint, and a correct label on the pallet.
Clarus has integration pages for the four big UK networks: Palletforce, Pall-Ex, Palletways och The Pallet Network. That means consignment data can go to the network from the same system that built and scanned the pallet, rather than being typed into a separate portal.
Cross-docking for pallet network members
Network depots and 3PLs that cross-dock deal with mixed pallets in both directions. Mathew Buttar describes a Clarus cross-docking automation where 26 inbound pallets can be split automatically into 13 deliveries of two pallets each, every one with its own pick list and dispatch. You decide whether a charge applies to a cross-dock pallet or not.
Common mixed palletising mistakes
Most mixed pallet problems come from a handful of habits. If your claims and refusals are creeping up, check these first.
- Picking in rack order, not stack order: heavy products slotted at the end of the walk sequence force upside-down builds. Fix the slotting before you blame the pickers.
- No pallet ID until dispatch: if the pallet only gets a label at the end, nobody can tell what’s on it if it’s split, rebuilt or misplaced on the way.
- Visual checking as the only control: it costs a second person on every load and still misses errors when the dock is busy.
- Ignoring the receiver’s rules: a store, a retailer DC and a pallet network hub may each want a different height, label or build order.
- Wrapping too high and too loose: wrap that doesn’t lock the bottom layer to the base lets the whole load slide.
- Treating part pallets as finished: rebuilt part pallets going back into racking need the same stability checks as outbound loads.
If you’re deciding whether your current system can support better mixed palletising, our guide to the best warehouse management system software sets out what to look for, and our guide för lager i plockning covers pick methods that feed pallet builds. Distributors with large trade ranges might also find our page on wholesale and distribution software useful, along with our overview of pick and pack for smaller orders. A standard Clarus implementation aims to go live in around 12 weeks with the right support on both sides.
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