How much lighter is a plastic case at the same cavity?

Answer: 3.3 kg at 25 L and 5.6 kg at 60 L, or 0.124 kg per litre against 0.256 kg. The saving is hardware, not wall.

Can an IP67 plastic case replace an IP54 flight case?

Answer: On sealing yes, on geometry and repair no. A foam strip cannot hold 1 m for 30 min.

Why is a flight case cheaper below 100 units?

Answer: Tooling. CNY 120,000 over 100 units is CNY 1,200 each, plus CNY 34 of resin and time, against CNY 300 with no tool.

What if volume is small but the seal must be IP67?

Answer: Use a cavity that already has a tool so tooling is zero, or order 500 in batches at CNY 274. One trades geometry freedom, the other stock.

Which corner survives a drop better?

Answer: At 1.5 m with 25 kg the plastic case peaks at 52 g with a scuff, the flight case at 68 g with 4 mm of deformation.

How is empty return volume counted?

Answer: A plastic case nests 1:2.8, so forty empties take the space of fourteen; a framed case counts 1:1.

Plastic Case vs Flight Case: Weight, Cost, Protection

Quick answer: At a 25 L cavity a plastic case weighs 3.1 kg against 6.4 kg for a flight case, seals to IP67 against IP54, and beats a flight case on unit cost past 500 units once tooling is amortised.

Where the two types diverge
Weight at 25 L and 60 L
Tooling versus extrusion and labour
What IP54 and IP67 actually buy
Drops, stacking and repair over time
Five checks that decide the line
FAQ

1. Where the two types diverge

A flight case is assembled; a plastic case is moulded. The first uses 20 mm aluminium extrusion, riveted corners and a 9 mm plywood panel. The second leaves one tool with lid, body and hinge as one part, sealed by a gasket in a moulded groove.

Joint count decides where water enters and how repairs go.

A flight case wall is frame, panel and corner, so damage is swapped piece by piece, paid for by a gasket that ages. A plastic case carries a continuous 2.8 mm wall, 4.2 mm at the corners, and absorbs a drop by deforming whole, at the price of one tool.

Item	Flight case	plastic case
Wall	Extrusion + 9 mm plywood	One shell, 2.8 mm
Seal	Foam strip	Two-lip silicone
Size	Any, 5 mm steps	Fixed by tool
Rating	IP54	IP67

2. Weight at 25 L and 60 L

At 25 L the flight case runs 6.4 kg against 3.1 kg moulded, a 3.3 kg gap; at 60 L, 11.8 kg against 6.2 kg. Per litre that is 0.256 against 0.124 kg and 0.197 against 0.103 kg, so the gap narrows as the case grows.

Plastic case: sand body across a workshop steel bench, vertical ribs and two latches on the flank, folding handle, empty shelving behind

Density explains part: aluminium 2.7, ABS 1.04, PP 0.91 g/cm³, while plywood at 0.65 is no culprit. Hardware is: extrusion, corners, latches and hinges add 4.1 kg on a flight case against 1.2 kg moulded.

On one case 3.3 kg is a rounding error; on forty it is 132 kg, charged every trip. Cube adds a layer: the frame stands proud, the outer box runs 8% larger, so forty units eat 0.6 m³ while a plastic case follows to 22 mm. The return leg separates them again, since a plastic case nests at 1:2.8 while a framed one stacks at 1:1. Four trips a month covers the price gap on a dozen cases in empty return freight alone. None of that shows on a quotation, only on the freight invoice.

Cavity	Flight case	plastic case	Per litre
25 L	6.4 kg	3.1 kg	0.256 / 0.124 kg
60 L	11.8 kg	6.2 kg	0.197 / 0.103 kg

3. Tooling versus extrusion and labour

Cost crosses over with volume, not unit price. Below 100 units the flight case wins: 3.2 m of extrusion, plywood, hardware, CNY 210 of material and CNY 90 of labour, no tool, CNY 300 each. A 25 L mould costs CNY 120,000, so 100 units absorb CNY 1,200 plus CNY 26 of resin and CNY 8 of moulding time, CNY 1,234.

Five hundred units is where the two lines meet.

At 500 the tool drops to CNY 240 and the case lands at CNY 274; at 2,000 it is CNY 60 and the case CNY 94, while the flight case only reaches CNY 285.

Volume	Flight case	plastic case
100	CNY 300	CNY 1,234
500	CNY 300	CNY 274
2,000	CNY 285	CNY 94

A paid-off tool still locks the cavity: reshape it and another tool is bought. A line changing cavity twice a year belongs with the flight case.

4. What IP54 and IP67 actually buy

IP54 stops solids over 1 mm and splashes; IP67 adds 1 m of water for 30 min. A flight case reaches IP54 with an 8 mm EVA strip that seals only at 30% compression, so a lid not pulled hard leaks.

Plastic case: sand shell open on a warehouse floor, egg-crate foam in the lid, inserts holding cartons, three latches and a handle

A plastic case reaches IP67 with a two-lip silicone gasket at 50 Shore A and 3.5 mm section, each lip forming its own line contact, plus a valve at 0.05 bar so breathing vents instead of lifting the lips.

EVA takes 18% compression set after 200 h at 60 °C and needs replacing at two years; silicone sets 6% and runs five years.

5. Drops, stacking and repair over time

A 1.5 m corner drop with a 25 kg payload: the aluminium corner feeds 68 g into the frame and deforms 4 mm, while the moulded corner at 4.2 mm absorbs it at 52 g, scuffed, not pierced.

Stacking is a lid test, not a base test.

A 25 L moulded lid carries 120 kg static for 24 h at 1.8 mm deflection, springing back to 0.4 mm; a plywood lid deflects 5 mm and the ABS skin lifts. Six high is the ceiling for both.

Repair splits them. A flight case panel is 40 min and CNY 180, a corner 25 min and CNY 60, strength back to ninety percent; a cracked plastic case is swapped whole at CNY 274 in two minutes. Odd geometry favours the flight case, standard cavities the mould.

6. Five checks that decide the line

Five checks settle most cases.

Under 100 units, cavity may change: flight case, CNY 300, no tooling risk.
Over 500 units with a stable cavity: plastic case, under CNY 274.
Submersion at 1 m: IP67, which foam cannot deliver.
Empty returns by air or sea: nesting at 1:2.8 pays back within a year.
On-site repair: a flight case takes a new panel, a moulded case is swapped whole.

One check on the plastic side re-runs the other four, and the reverse holds too.

Conclusion

Three lines, three crossovers. The 3.1 kg against 6.4 kg at 25 L is decided by hardware; CNY 1,234 against CNY 300 at 100 units by tooling; IP67 against IP54 by silicone lips against a foam strip. What remains is the lane itself: volume, how often the cavity changes, whether the case gets submerged, whether empties fly back. The heaviest of the four decides, and the other three confirm it.

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.