How thick should a hard protective case be?

Answer: A 3.0 mm side wall at 110 mm pitch carries 25 kg through a 1.2 m drop. Below 2.4 mm with heavy contents, ribs cannot close the gap.

Do more ribs make a case stronger?

Answer: No. Under 70 mm pitch the lid shows sink marks and weight climbs; above 10 mm the ribs take the stacking load and crush first.

Can compression results replace drop testing?

Answer: No. Compression measures creep under a long load, drop measures instantaneous impact; a lid holding 1,200 N may still fail a corner drop.

When is a hard protective case the wrong choice?

Answer: When drops stay under 0.5 m, trips under 20 a year, and nothing is stacked on top; a 3 mm EVA bag covers it.

How many latches are enough?

Answer: One per 200 mm of rim, so a 600 mm rim takes three. Fewer leaves the gasket unevenly compressed and the seal leaks.

Hard Protective Case Selection: 5 Criteria That Decide

Quick answer: Judge a hard protective case by what the shell can take: wall thickness and corners, rib pitch, compression and drop results, latch and gasket retention, and whether a soft bag would do. The first four show up in a sample and a test report; the fifth stops you paying for rigidity you never use.

Five criteria for a hard protective case
Criterion 1: wall thickness and thickened corners
Criterion 2: rib pitch and direction
Criterion 3: compression, drop and cold impact
Criteria 4 and 5: latches, sealing and the soft-bag boundary
FAQ

1. Five criteria for a hard protective case

The line between a hard case and a soft bag is not surface feel but whether the shell keeps force outside the wall: the shell takes the impact, the insert spreads what is left.

Read inward: thickness and corners decide how much material exists, ribs place it, compression and drop prove both, latches hold the closing face.

Criterion	Measure	Acceptable line
Thickness	Wall and base	3.0 mm plus or minus 0.3
Ribs	Height and pitch	120 mm or less
Compression	Lid load	2 mm or less
Latches	Retention	1.5 kN or more
Soft-bag boundary	Drop height	Below 0.5 m

2. Criterion 1: wall thickness and thickened corners

A hard protective case commonly runs a 3.0 mm side wall, 3.6 mm base and 2.8 mm lid for 25 kg. Read 30 mm below the rim and above the base, then judge by the lower figure.

Hard protective case in olive green facing the camera, lid ribs stacked across the top, two latches clamping the rim, thickened corners bulging

Nine readings should agree within 0.3 mm; a wider spread means uneven mould temperature; the thin patch is where a drop cracks. Corners thicken to 4.5 mm, 60 mm down and 40 mm across.

Zone	Gauge	Note
Side wall	3.0 mm	No cold-drop crack
Base	3.6 mm	Light corner scuff
Lid	2.8 mm	0.5 mm centre dish

3. Criterion 2: rib pitch and direction

Ribs turn a point load into a surface load. On a 2.8 mm lid, 8 mm height at 110 mm pitch with a 1.8 mm root holds; under 70 mm pitch, sink marks appear opposite the rib root.

Hoop ribs resist bulging, longitudinal ribs resist bending, crossings want an R3 fillet. Above 10 mm height, stacked weight lands on rib tops and the ribs crush before the lid.

4. Criterion 3: compression, drop and cold impact

Compression runs across the whole lid face: 1,200 N for 24 hours with 2 mm deflection or less. Stacked six high at 130 kg a case, the bottom unit carries 650 kg, not the single-point static rating.

Hard protective case in dark grey angled to show wall thickness, vertical ribs from rim to base, two wide latches biting the joint

Drop testing runs ten drops at 1.2 m over six faces, three edges, one corner at 25 kg. After four hours at minus 20 C, polypropylene keeps about sixty percent of its impact strength.

Test	Condition	Pass
Compression	1,200 N, 24 hours	2 mm or less
Stacking	Six high, 130 kg	No set
Drop, cold	Minus 20 C, four hours	No corner crack

5. Criteria 4 and 5: latches, sealing and the soft-bag boundary

Latches run 1.5 kN retention and 60 to 90 N to open, higher than a tote box because the gasket compresses first. A 4 mm gasket wants 30 percent squeeze; at 50 percent it hardens and leaks.

The soft-bag boundary is where a hard protective case can lose the argument: Below 0.5 m of drop and 20 trips a year, a 3 mm EVA bag weighs a third of a hard shell; above 0.8 m with stacking, rigidity earns its cost.

Condition	Hard protective case	Soft bag
Drop height	Above 0.8 m	Below 0.5 m
Trips a year	Over 20	Under 20
Stacking	Six high	No

Conclusion

Five criteria come down to one sentence: the shell has to take the hit. Thickness and corners supply material, ribs place it, compression and drop supply evidence, latches defend the closing face, the soft-bag boundary removes unwanted rigidity. What you buy in a hard protective case is certainty about that one impact.

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.