Unitization and Stacking

The unitization and stacking of packages typically occurs in three basic forms:

  1. The single load pallet.

  2. The mixed load pallet.

  3. The mixed load, bulk container.

Many products may be, during their distribution chain, shipped in a mixed load. Your choice of materials should take this into consideration. It may occur that a given product will travel first on a single product unitload, next in a mixed load and finally as an individual parcel. Compression strength is usually the important factor for the first two legs of the journey and high bursting strength is often more important for the last leg.

Overhang occurs at three possible points in a unitized load:

Cases overhanging the pallet - the worst type of overhang. Always try to avoid this type of overhang for three reasons:

  1. Reduction of stacking strength.

  2. Elimination of layout options in aircraft and trucks.

  3. Increased hazard to damage due to pallet marshalling.

Cases offset - upon each other due to either poor stacking or loose stretch film or bands will loose much of their stacking strength as well as exposing corners and edges to additional hazards. Corner boards and stretch wrap film greatly reduce the tendency for this to happen.

Cases overhanging a deck board - This also diminishes the stacking strength of the case. This is a concern with both top and bottom deck boards. Adequate coverage of deck boards helps this problem.

Stacking Hazards
Load distribution can be deceptive.

The illustration left highlights the fact that while it  may seem
that the greatest weight falls on the bottom cases of the
bottom pallet, in fact due to the small area of the top pallet's
runners, the greatest load distribution falls on the top layer
of the bottom pallet.

Interlocking pallet stacking patterns reduces the compression strength of the unit load significantly. In situations where product support is negligible it should be avoided if possible. However, interlocking stacking patterns make the load more stable in transit. Ways to improve stack stability include: Stretch wrapping either mechanically or via narrow width hand-wrappers, stretch banding, heat shrink wrapping or bagging and break-away palletization adhesives.

A Pallet with a single case size, protected and secured. This is the most common form of load preparation. Often the load will include the additional protection of top boards and corner protectors, as illustrated below. The load is usually two or four way banded, but may also be shrink or stretch wrapped. Unitization options can also include anti slip agents between cases.

Unitload bulk container attached to pallet - This method of unitization is appropriate for mixed products that must travel as a unitload in challenging shipping environments. Voids could be filled by Kraft paper, braced by empty boxes marked as "empty box" labels and/or corrugated modular braces. The Case minimum material requirement should be established, and an example is show below and should sustain stacking 3 loads high for 3 months at 80% humidity. Metal and plastic cages are often also used for this task, they have the advantage of enabling a higher stack height in non-racking warehouse facilities, but can prove expensive if there is a low return rate in the distribution chain.

Bulk Container on a Pallet Example

  Case Pallet Unitload
Dimensions MM 800 x 600 x 600 - O.D. 800 x 600 x 144 800 x 600 x 744
Dimensions Inch 31.5 x 23.62 x 23.62 31.5 x 23.62 x 5.67 31.5 x 23.62 x 29.3
Recommended Max. Wt. Kg. 85 Kg. 15 Kg. 100
Recommended Max. Wt. Lbs. 187 Lbs. 33 Lbs. 220
Recommended Material 48 ECT DW 42/26/33/26/42 Euro Pallet  

Bulk Container on a Pallet


Mixed Loads

Unitizing Methods - Whenever possible mixed loads should be built as shown below in column or layer patterns. This may not be possible most of the time, but should be followed as closely as possible to maximize strength and weight distribution.

Layer Stacked - note the even distribution of packs with the same height in the different layers of the load. Column Stacked - Note that similar cases are stacked in there own columns.



There are numerous sizes and types of pallets, below are a list of some of the most common kinds that you may encounter.

Euro Pallet - Block Style GMA - notched

Some Typical Sizes

  1. Standard (Europe) 1200mm x 1000mm x 144mm
  2. Euro 1200mm x 800mm x 144mm
  3. Half Euro 800mm x 600mm x 144mm
  4. GMA Style 48" x 40" x 5"

For guidance performance parameters as defined by the Chemical Industry Pallet Specification as shown below:

Chemical Industry Pallet Spec

1. Recommended nominal base dimensions +3mm(1/8") tolerance:

Metric Sizes US equivalent nominal sizes
1200 x 1000mm 48" x 40"
1200 x 800mm* 48" x 31.5"
1300 x 1100mm 52" x 44"
1140 x 1140mm 45" x 45"
2000 x 1000mm* 80" x 40"

* Also commonly used sizes.

2. Maximum recommended platform height 155 mm(6").

3. Square in each direction. NOTE: The difference in length of the two diagonals should not exceed 13 mm(1/2").

4. Four-way, partial four-way, or two way entry.

5. Should be capable of accommodating pallet jacks. Note: For acceptable performance it is recommended that pallet jack openings have a minimum width of 305mm(12") and a minimum height of 95.mm(3 3/4) when under maximum load. The bottom surface should have 305 mm(12") square openings properly placed for pallet jack wheels. The center support should be a maximum of 155 mm(6") wide

6. Top and bottom bearing surfaces should be designed to support the intended weight and package type; be flat, non-skid and have no indentations or protrusions that could cause product damage. NOTE: For acceptable performance it is recommended that the top bearing surface have a minimum coverage of 62 percent and the bottom bearing surface have a minimum coverage of 45 percent.

7. Maximum recommended deflection of loaded pallet if racked: 12 mm(1/2").

8. No protruding fasteners.

9. Should be made of recyclable materials.

10. Compatible in at least one direction with pallet conveyors, dispensers and automatic storage/retrieval systems.

11. Minimum recommended load capacity: One metric ton.

12. Should be capable of multiple stackings.

13. Should be capable of multiple trips.

14. Should be capable of safely moving product through it entire distribution system.

Additional Protection for Unitized Loads


Slipsheets are placed on the top of the pallet between the product and the pallet. They protect the product in poor warehouse and transportation conditions as well as helping to spread the load on pallets that are not full decked. Typically they are made of B or C flute, the corrugation direction is optional. The performance of the slipsheet is judged by its bursting strength, which preferably should be no less than 200T Mullen (1379 kPa). The use of water resistant liners, while often more expensive can be advantageous if moisture is a problem in the shipping environment.

Cap / Top Board

A protective cap and/or top board is recommended for added protection against stacking and moisture damage. If it is to provide protection against these threats the material should be specified, please see the specification section of this KnowledgeBase. Often large sections of corrugated board are used, however for more challenging distribution chains the use of chipwood might be considered.


As mentioned earlier, Shrinkwrap, or more usually stretchwrap, can be used to help stabilize a load and give additional environmental protection. An example of the specification for a typical, good stretchwrap film is shown below:

Polyethylene 80 gauge (.8 mil) Minimum 250% pre-stretch

Properties (Units) ASTM Test Values
Gauge (MIL)   0.8
Haze (%) D1003 < 3.0
2% Secant Modulus (KPSI) D882  
MD   18.9
CD   3.1
Tensil Ultimate (KPSI) D882  
MD   4.8
CD   575
Tensile Elongation (%) D882  
MD   440
CD   575
Elmendorf Tear (GM) D1922  
MD   250
CD   500

Corner protection

Corner protection, please see the illustration for "A Pallet with a single case size, protected and secured" above, is recommended for all non-bulk packed unit loads. The corner protector should be as close to the full height of the load as possible, and preferably not less than 6" (150mm) from the top of the unit load.


Strapping or banding is another excellent way of securing loads. We would recommend that all internationally shipped unitloads or unitloads bound for air cargo should be banded with 4 bands (2 x 2). Please see the illustration below.