Item Properties
Every item in LOP carries a set of properties that control how the optimizer places it and how the constraint engine validates the resulting load plan. Understanding what each property does helps you build more accurate load plans and avoid unexpected results.
Weight
Field: Weight (kg or lbs, depending on your unit preference)
Weight is one of the most consequential item properties. It is used in three distinct ways:
Payload enforcement — The sum of all item weights in a container must not exceed the container's maximum payload. If the total weight exceeds the limit, the optimizer will attempt to distribute cargo across additional containers.
Center of gravity calculation — The optimizer calculates the weighted centroid of all placed items to determine whether the load is balanced. Heavier items placed too far to one side will degrade the Weight Balance score and may trigger a balance warning.
Stacking safety — When one item sits on top of another, the optimizer checks the cumulative weight bearing down against the lower item's crush strength. If the weight exceeds the crush limit, the placement is rejected.
Always enter the weight of one unit of the item as it will be loaded — including all packaging, pallets, and internal contents. A weight of zero is technically valid but will cause the optimizer to ignore this item's contribution to the center of gravity calculation, which can result in misleading balance scores.
Fragile
Field: Fragile (toggle)
When an item is marked fragile, the optimizer enforces a hard constraint: no other item may be placed on top of it. This applies regardless of the stacking or weight settings of the item above.
Fragile items are visually distinguished in the 3D viewport to make the load plan easy to review.
Use this setting for:
- Glass, ceramics, or delicate electronics
- Items in thin-walled packaging that cannot bear any load
- Any cargo where stacking from above would risk damage
Stackable
Field: Stackable (toggle)
Stackable controls whether other items are permitted to rest on top of this item. When stackable is turned off, no items will be placed above this one.
The distinction between Fragile and Stackable is intentional:
| Can have items placed on top? | Can be placed on top of other items? | |
|---|---|---|
| Fragile = true | No | Yes |
| Stackable = false | No | Yes |
| Both | No | Yes |
In practice, most items are stackable. Turn stackable off for items that cannot structurally support weight from above — for example, a hollow plastic container or an irregularly shaped item that would create an unstable base.
Setting Stackable to false is a hard constraint. The optimizer will never place any item on top of a non-stackable item — this is enforced strictly during both initial placement and optimization refinement. You do not need to also set Max Weight on Top to 0.
Max Weight on Top
Field: Max Weight on Top (kg or lbs, or leave blank for unlimited)
This is a hard stacking limit expressed as a weight. It defines the maximum cumulative weight that may be placed on top of this item. The optimizer treats this as an inviolable constraint — any placement that would cause the weight on top to exceed this value will be rejected.
Leave this field blank (or set it to null) to indicate that this item has no stacking weight limit.
Max Weight on Top and Crush strength are two separate fields with two different units. Max Weight on Top is a total weight in kg. Crush strength is a pressure in kg/m²: the load above is divided by the item's top-face area before it is compared against the limit. Both are enforced as hard constraints, and you can set either, both, or neither. See Crush Strength.
Practical guidance:
- A standard wooden pallet can typically support 1,000–2,000 kg on top
- A corrugated cardboard carton of average quality supports roughly 100–300 kg depending on stacking pattern
- Drums of hazardous liquids typically have manufacturer-specified stack limits — use those values directly
Crush Strength
Field: Crush strength (kg/m², or lb/ft² with imperial units; leave blank for unlimited), beside Max Weight on Top in Add Item and in the Item Library
The supplier's pressure limit for the item's top face. The load resting above the item is divided by the area of its top face, as placed, and compared with this value. Like Max Weight on Top it is a hard constraint: the optimizer does not place a load that would exceed it, and Validate reports any layout that does. A value of 0 means nothing may rest on the item; a blank field means no limit.
Enter the limit the supplier states for the item in transit. A box compression test (BCT) result does not belong here: a BCT is the force at which a box fails in the laboratory, not a load it should carry. Record it in the Carton section instead.
Packaging and Carton Data
Field: Packaging (Not specified · Corrugated carton (RSC, FEFCO 0201) · Other packaging), with a collapsed Carton section when Corrugated carton is chosen
LOP never assumes that a box is a corrugated carton. When you choose Corrugated carton, the Carton section records what the supplier sheet or the lab report states:
| Field | What to enter |
|---|---|
| Strength data | Where the strength figures come from: the supplier's working limit (entered in Max Weight on Top or Crush Strength), a measured box compression test (BCT), or board data (ECT and thickness) |
| Board · Flute | Single, double or triple wall, and the flute profile (for example C, or BC for double wall) |
| Measured board thickness | The combined board thickness (caliper) in mm, as measured |
| Edge crush strength (ECT) | The value, its unit (kN/m or lbf/in) and the test method. The other unit is shown beside the input (32 lbf/in = 5.6041 kN/m); LOP stores the value in the unit you chose |
| Flutes vertical along | The item axis that is vertical when the flutes stand upright |
| Item dimensions are the carton's outside dimensions | Yes or No. LOP does not assume either |
| Closure · Holes | How the box is closed (tape, glue, staples), and any hand holes or vents |
| Measured box compression (BCT) | The value, its unit (N, kN, lbf or kgf) and the test method (for example ASTM D642 or ISO 12048) |
| Test conditions | The test temperature and relative humidity, the test date, and whether the contents support the load |
| Source | The supplier sheet or lab report the values come from |
A blank field stays unknown; it is never read as zero. A value without its unit is not accepted, and no grade is filled in for you.
With the plan's transit conditions entered, Validate calculates a compression estimate from carton data, as soft cards only (Carton compression (calculated)). Carton data never change how the optimizer packs, and they never replace Max Weight on Top or Crush Strength, which stay the hard limits.
Carton data travel with the item when you add a library item to a plan, save a plan item to the library, duplicate a plan item, or create a template from a plan. Like Crush Strength, they are among the fields a plan refreshes from the library when it opens.
Orientation
Field: This side up (checkbox in Add Item and the Item Library)
For cuboids, checking This side up keeps the item's height axis upright; unchecking it selects Auto.
| Preference | Allowed cuboid rotations |
|---|---|
| Auto | All six length, width and height arrangements. |
| This Side Up | Two rotations, LWH and WLH: the height stays up and the footprint can turn 90 degrees. |
| Vertical Only | LWH only: the item's own height stays up and its footprint does not turn. |
| Horizontal Only | LHW, HLW, WHL and HWL: the item's own height axis lies horizontally. |
Vertical Only and Horizontal Only can be set through spreadsheet import; editing other properties preserves them until you explicitly toggle the checkbox.
Cylinders use three solver orientations, and STEP parts keep their saved pose rather than using these cuboid rotation codes.
Overly restrictive orientation settings reduce the optimizer's ability to find efficient packings. Use This Side Up when physically required (liquids, fragile surfaces, printed labels that must be readable) rather than as a general precaution. For most solid cargo, Auto will produce the best results.
SKU
Field: SKU (optional text)
A stock-keeping unit identifier. This field is purely informational — the optimizer does not use it. The SKU is stored with the item and included in all CSV and Excel exports, making it easier to cross-reference the load plan with your warehouse management system.
Notes
Field: Notes (optional text)
A free-text field for any additional handling instructions or contextual information about the item. Notes appear in exported load plan reports and PDF documents.
Examples of useful notes:
- "Keep dry — do not stack on floor without pallet"
- "Lithium battery — see IATA Section II declaration attached"
- "Customer priority — load last for first delivery"
Separation Tags
Field: Separation Tags (multi-select)
Separation tags enforce minimum physical distances between incompatible cargo types. This is primarily used for hazardous materials compliance and food safety segregation.
When two items in the same container have incompatible tags, the optimizer calculates the center-to-center distance between their placements and checks it against the required separation distance. If the constraint cannot be satisfied, one of the items is marked as unplaced.
Built-in separation rules:
| Tag Combination | Minimum Distance |
|---|---|
hazmat_class_1 ↔ hazmat_class_2 | 3 meters |
Any hazmat ↔ food | 5 meters |
wet ↔ food | 3 meters |
Separation constraints are hard constraints — they cannot be relaxed by the optimizer. If your container is too small to satisfy all separation requirements simultaneously, some items will be left unplaced. In that case, consider using multiple containers and assigning incompatible cargo to separate containers entirely.
You can assign multiple tags to a single item. For example, a drum of industrial cleaning fluid might carry both hazmat_class_3 and wet.
Library Items and Your Plans
When you add an item from the Item Library to a plan, LOP keeps that plan in sync with the library definition. Editing the item's synced fields in the library later automatically updates every plan that already uses it the next time the plan is opened, so your plans track your current product specifications. A dimension change resizes the item's boxes where they stand, without moving any item, and the plan shows a soft "Layout outdated — re-solve" banner in the score panel until you re-optimize. Re-solving re-places loose items and moves loaded pallets in the container; it does not re-pack their contents. A pallet or rack holding the item shows Review placement or Re-pack needed instead — see When Item Dimensions Change.
For a library-linked item, in-plan edits do not write back to the Item Library. On every editor open, the library values replace all synced fields in the plan: dimensions, canonical orientation, weight, stackability, fragility, maximum weight on top, crush strength, carton data, orientation preference and color. An in-plan edit to any of these fields lasts until the plan is next opened; edit the library item to make the change permanent.
Setting Properties via Import
You can set Stackable, Fragile, and Max Weight on Top directly from your Excel or CSV file during import. Include columns with these names in your spreadsheet — LOP recognizes them automatically.
- Stackable and Fragile accept:
1/0,yes/no,true/false - Max Weight on Top accepts a numeric value in kg or lbs
See Importing from Excel or CSV and AI Smart Detection for more details.
Group ID
Field: Group ID (optional text)
Group ID is used to keep related items physically close to each other in the loading plan. Items sharing the same Group ID will be placed near each other whenever the optimizer can do so without significantly reducing overall utilization.
This is a soft constraint — the optimizer will try to honor grouping, but will not sacrifice a significantly better overall placement to enforce it. See Quantity & Groups for more detail and best practices.