A drawing that says “4 mm PP board” describes almost nothing. Thickness is one of six properties that determine how the part will behave, and the other five get decided by whoever supplies the material that week.
The result is a part that was qualified with one board and is produced with another, and a problem that appears a year later with no obvious cause.
The six lines
1. Thickness, with tolerance. The fit dimension. State the range, not the nominal figure.
2. Gram weight, with tolerance. The closest thing to a strength proxy that is easy to verify on delivery.
3. Structure. Corrugated or honeycomb, and for corrugated the flute pitch or count. This is what determines stiffness in the flute direction and it is almost never stated.
4. Flute direction relative to the part. The single most consequential omission. Write it against a dimension on the drawing rather than leaving it to convention.
5. Colour, with a reference. Either a retained sample or a colour reference. If the part is not visible, “any” is a perfectly good answer and saves money.
6. Additives and service conditions. UV stabilised for outdoor use, antistatic for electronics, fire-retardant grade if a requirement applies, and the temperature range the part sees.
What to add if the part is bonded or printed
Two more lines. Whether the board has to be surface treated, and how recently – because treatment decays and a treated board from last quarter is not the same material. If the part is bonded or printed, this is not a detail; it is the whole reason the process works.
What not to specify
Brand names, where a generic board would do. Specifying a brand narrows your supply, raises cost and creates a dependency for no functional benefit. Specify the properties and let the material be chosen to meet them.
Equally, do not specify a tighter tolerance than the function needs. Over-specified tolerances are paid for on every part and benefit nothing.
Writing it so it cannot be misread
The test of a specification is whether two people reading it would buy the same material. A line that says “4 mm PP corrugated, flutes running along the 600 mm dimension, white, UV stabilised, 600 gsm plus or minus 5 percent” leaves no room. A line that says “4 mm PP board” leaves all of it.
If you only change one thing on an existing drawing, add the flute direction. It is the line most likely to be missing and the one most likely to explain a performance difference.
Two worked examples
Abstract guidance is easier to use once it has been filled in. Here is the same specification discipline applied to two very different parts.
A divider inside a returnable tote. Material: polypropylene, copolymer. Construction: corrugated profile. Thickness: 3 mm, tolerance plus or minus 0.2 mm. Colour: grey, near enough is fine. Additives: none. Orientation: flutes vertical when installed. Nothing else is required. Six lines, and a supplier reading them knows exactly what to quote.
A load-bearing panel in a dunnage tray. Material: polypropylene homopolymer, virgin, no regrind in the skins. Construction: honeycomb, cell size 8 mm. Thickness: 10 mm, plus 0.3 minus 0. Surface: both faces untextured. Additives: UV stabilised, light fastness sufficient for intermittent outdoor exposure. Orientation: cell axis parallel to the 600 mm edge. Performance: supports 40 kg distributed over the panel at 20 degrees Celsius and minus 10 degrees Celsius without permanent set greater than 1 mm. Evidence: three samples per production batch, retained, dated.
Same discipline, very different amount of detail, because the consequences differ. The second specification costs more to write and produces a part that costs more per unit – and is still cheaper overall than replacing a tray that creeps out of tolerance in the first summer.
What we can do
We supply corrugated PP sheet and will read your specification against what we would recommend, flagging anything that is missing or unnecessarily tight. If you have an existing drawing with only a thickness on it, send it over and we will tell you what else the part needs.