Is a rotomolded case always tougher?

Answer: For drops, yes; for static load, no. The 6 mm corner and the absence of weld lines win at 1.5 m, but a ribbed 2.8 mm body holds rim deflection to 4.5 mm and stacks well.

Can an injection molded case pass a 1.5 m drop?

Answer: Yes, with PC or PC/ABS at about 45 kJ/m² notched impact at −20 °C, at the cost of 260 °C melt, 80 °C mould temperature and 20 to 30 percent more per part.

Why is a 6 mm rotomolded case nearly twice the weight?

Answer: Density differs by a tenth while thickness more than doubles: HDPE near 0.94 g/cm³, ABS near 1.05 g/cm³. Trimming the mass means a smaller cavity or a 5 mm wall with more deflection.

Which process suits a 200-unit order?

Answer: Rotomoulding: EUR 37.50 of tooling per unit on top of a EUR 16 part, against EUR 291 for injection.

Can gaskets and latches be shared?

Answer: Rarely. A rotomolded case takes an 8 mm cord gasket in a moulded round groove; an injection moulded case takes a 5 mm flat gasket in a narrow channel. Hole pitch differs too.

Rotomolded vs Injection Molded Case: Wall, Impact, Cost

Quick answer: Rotomolded vs injection molded case comes down to three figures: 4 to 8 mm walls against 2.2 to 3.2 mm, a 1.5 m loaded drop at −30 °C that only whitens against 40 percent impact retention at −20 °C, and tooling at EUR 7,000 to 11,000 against EUR 44,000 to 68,000. The third sets the volume at which you switch.

One Shell or Two Halves
Wall Thickness, Stiffness and Weight
Impact: Drop Height and Fracture Face
Unit Cost and the 8,000-Unit Crossover
Four Site Conditions That Decide It
FAQ

1. One Shell or Two Halves

Injection moulding needs two cavities: lid and base are shot separately, then hardware is fitted. Rotational moulding charges powder into one tool, heats it on two axes, and the shell leaves the oven as one piece.

Cycle time decides the rest. Injection runs 60 to 90 seconds per shot, so a 650-tonne press makes about 800 lids a day. Rotomoulding takes 22 to 28 minutes, with a 4:1 axis ratio and 260 to 300 °C oven air. Twenty times the cycle cannot be recovered on machine rate, only on cheap tooling and low volume.

The process also leaves marks on the part. An injection moulded case carries a parting line, a gate mark and a rib grid, and holds ±0.2 mm. A rotomolded case has no weld line and low built-in stress, but wall thickness follows the powder charge, so ±0.8 mm is normal.

Item	Rotomolded case	Injection molded case
Forming	Powder fused on two axes, one shell	Lid and base shot separately
Cycle	22 to 28 min per mould	60 to 90 s per shot
Tooling	Welded aluminium, EUR 7k to 11k	Steel mould, EUR 44k to 68k
Wall	4 to 8 mm, set by powder charge	2.2 to 3.2 mm, set by cavity
Tolerance	±0.8 mm	±0.2 mm

2. Wall Thickness, Stiffness and Weight

Two 60-litre cases, same cavity. The rotomolded body runs a 6 mm wall at 8.2 kg; the injection moulded body runs 2.8 mm with 1.4 mm ribs at 4.6 kg. Across 500 units by air, the 3.6 kg gap is 1.8 tonnes of chargeable weight.

Rotomolded vs injection molded case from the inside: white case fully open on a steel bench, lid upright showing the black gasket ring, three latches on the lid edge

Stiffness is not thickness alone. Second moment of area scales with the cube of wall thickness, so 6 mm against 2.8 mm should be 9.8 times stiffer; the rib grid cuts the panel into 100 mm cells and measured rim deflection differs by two to three times.

Corners are where the rotomolded shell wins for free. An R25 cavity radius lets powder pool, so the corner measures 1 to 1.5 mm thicker than the flat wall — exactly where a dropped case lands. Injection can only thicken a corner with material, which sinks, so the fix is a 2 mm corner rib.

Same 60-litre format	Rotomolded	Injection molded
Wall	6 mm, ±0.8	2.8 mm, ±0.2
Empty weight	8.2 kg	4.6 kg
Rim deflection at 25 kg	2.1 mm	4.5 mm
Loaded drop passed	1.5 m	1.2 m

Gauge 12 points around the rim and 12 across the base, and judge the minimum: rotomoulded walls run 0.5 mm thin on the cold side, and a 60-litre case under 4 mm bulges by the third tier of a stack.

3. Impact: Drop Height and Fracture Face

Rotomoulded bodies are HDPE or LLDPE, brittle near −70 °C; a loaded 1.5 m drop at −30 °C whitens the corner without splitting it. Injection moulded bodies are usually ABS, which keeps 40 percent of notched impact at −20 °C, and the same drop leaves a flat, glossy face. That is brittle failure, not a scuff.

A drop report means nothing without height, faces and ballast. An empty case at 1.5 m and a 25 kg case at 1.5 m are different tests.

Five criteria belong in the order:

Height by mode: 1.2 m parcel, 0.9 m sea stacking, 1.5 m air freight
4 hours at −25 °C before the drop for northern projects
Ten drops over six faces, three edges and one corner
Ballast at 110 percent of load, so 25 kg is dropped at 27.5 kg
Pass means hardware intact and no ingress; whitening is allowed

One quieter point: a rotomolded shell gives a crack no weld line to follow. On an injection moulded case, the handle and latch bosses sit where melt fronts meet, and those two spots fail first.

4. Unit Cost and the 8,000-Unit Crossover

Cost has two halves. Rotomould tooling is welded aluminium at EUR 7,000 to 11,000; an injection mould runs EUR 44,000 to 68,000 and needs a 650-tonne press.

Rotomolded vs injection molded case, injection side: black closed case standing on a white surface, moulded handle recess in the lid, red rubber corner bumpers

Cumulative volume	Rotomolded (EUR 7.5k tool, EUR 16/part)	Injection molded (EUR 56k tool, EUR 10.5/part)
200	EUR 53.5	EUR 291
1,000	EUR 23.5	EUR 66.5
5,000	EUR 17.5	EUR 21.7
10,000	EUR 16.8	EUR 16.1

The lines cross near 8,000 units. Below it, tooling pushes injection into three figures per case; above it, 22 minutes of oven time turns from advantage into overhead.

Two costs escape quotes. Moving a rib on an injection mould costs EUR 2,500 to 5,000, against under EUR 400 for a new aluminium plate. Freight adds about EUR 4 per case by air for the heavier body.

5. Four Site Conditions That Decide It

Process choice follows four hard conditions. Miss one and the answer flips:

Below −25 °C in service: rotomoulded
Over 8,000 units a year where weight is charged: injection moulded
±0.2 mm assembly, metal inserts or a clear window: injection only
Above 120 litres or 15 kg per unit: rotomoulding, whose tooling grows slowly with size

Never mix hardware across the two. Latch seats are moulded at ±0.15 mm on an injection body and drilled at ±0.5 mm on a rotomolded one; the same latch seals one and sits loose on the other, and the leak appears in the rain, not on the bench.

Sampling settles it faster than a datasheet: three ballasted units each, ten drops.

Conclusion

Wall thickness sets the protection ceiling, impact behaviour decides whether cold and drop conditions are met, and tooling amortisation decides the volume at which you switch. 8,000 units is the cost line, ±0.2 mm against ±0.8 mm the accuracy line, −25 °C the material line.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.