How much allowance does a custom foam insert protective case need?

Answer: 3–5 mm per side in plan plus 30–35 mm of depth for the layers.

Is higher EVA density always better?

Answer: Only when it matches the item weight. At 80 kg/m³ around a 3 kg item, shock still reaches the load.

What is the thinnest wall between cavities?

Answer: 8 mm, and only between items under 2 kg; thinner collapses under a die.

Can one insert drawing serve rotomoulded and injection-moulded cases?

Answer: No. Rotomoulded cavities move 2–3 mm more, so clearance and coordinates both change.

At what stack height is a pallet needed?

Answer: Above five layers; at seven, lid sag passes 5 mm and the foam loses preload.

Custom Foam Insert Protective Case: Size, Wall Thickness, Load

Quick answer: A custom foam insert protective case is specified from the inside out: measure the item, set the cavity, then add 3–5 mm of clearance per side, the foam layers and the wall. Clearance wrong and the insert will not go in; wall thin and the stack collapses.

Sizing a Custom Foam Insert Protective Case from the Inside Out
How Much Clearance the Insert Needs
Layer Stackup, Density and Hardness
Cutting Methods and Minimum Wall Between Cavities
Case Wall, Outer Size and Stacking Load
FAQ

1. Sizing a Custom Foam Insert Protective Case from the Inside Out

Enquiry sheets open with an external size of 600 × 400 × 230 mm because it is easy to measure. Build to it and the cavity shrinks to 520 × 330 × 180 mm, too small for the item.

Cavity figures belong at rim and base. Injection mouldings carry 1.5–2° of draft, so a 200 mm deep case is 3 mm narrower per side at the bottom; rotomoulded bodies lose 5 mm.

Only then does the layer split matter.

Material	Density (kg/m³)	Hardness	Layer
PU convoluted foam	20–30	Very soft	Lid
EVA foam	38–80	Shore A 25–45	Cut cavity
PE crosslinked foam	35–60	Shore C 40–60	Base

Two EVA sheets both marked 45 kg/m³ can feel a grade apart, so a custom foam insert protective case drawing needs density, hardness and thickness side by side.

2. How Much Clearance the Insert Needs

Clearance is the gap between insert and cavity wall, 3–5 mm per side, built from ±2 mm moulding variation and ±1 mm die cutting.

Custom foam insert protective case: macro view of dark grey foam cell walls, grainy skin texture, open cells fading out of focus

3 mm suits an injection-moulded PP body; 5 mm suits rotomoulded PE, whose 5–7 mm wall shrinks more freely.

Clearance handles wall fit, compression handles the item: 10–15% side interference holds the load still, and the lid foam adds 3–5 mm of preload.

3. Layer Stackup, Density and Hardness

A custom foam insert protective case usually carries 20 mm of PE base foam, an EVA cavity layer and 15 mm of PU foam in the lid; that 35 mm comes off cavity depth first.

Density follows unit weight: 38–45 kg/m³ below 3 kg, 50–60 up to 10 kg, 65–80 above. A 600 × 400 mm set moved from 45 to 70 gains 0.6 kg.

Shore A 25–45 for EVA and Shore C 40–60 for PE do not convert. EVA stiffens 8 Shore A at −20 °C and creeps above 60 °C, so cold-chain work wants 1 mm more per cavity side.

4. Cutting Methods and Minimum Wall Between Cavities

Die cutting suits 200+ pieces and cuts up to 80 mm deep at the lowest cost; CNC routing covers deep pockets; waterjet leaves no heat-affected edge.

Custom foam insert protective case: black case closed on a workshop bench, one wide latch, two grey cut foam liners behind, a knife beside

Minimum wall between cavities is most often left off the drawing: 8 mm under 2 kg, 10–12 mm normally, 15 mm above 10 kg.

Cavities run 2–3 mm shallow so the lid presses the top face, corners at R3–R5, with a finger notch between neighbours.

Item weight	Base foam	Wall between cavities	Process
Under 2 kg	15 mm	8 mm	Die cutting
2–10 kg	20 mm	10–12 mm	CNC routing
Over 10 kg	25 mm	15 mm	Routing or waterjet

5. Case Wall, Outer Size and Stacking Load

Outer size chains from the cavity: plus foam, clearance, wall and latch protrusion. A 520 × 330 × 180 mm cavity with 10 mm foam, 3 mm clearance and a 3 mm wall makes 552 × 362 × 218 mm outside.

PP walls run 2.5–3.5 mm, 4.5 mm at rib roots; PE 5–7 mm with corners no tighter than R8. Each millimetre adds 0.35 kg on a 600 × 400 body.

Load is pressure on the base: 25 kg over two pads should compress under 2 mm, and 4 mm means the item has reached the shell.

Five cases high put about 100 kg on the bottom unit and sag its lid 2–3 mm; ribs or a pallet hold it. From 1.2 m onto six faces, three edges and a corner, a custom foam insert protective case needs 3 mm of residual compression.

Conclusion

The specification of a custom foam insert protective case is an addition chain from the inside out: cavity from the item, clearance from tolerance, layers from weight, wall from stacking load. Put those four numbers on one drawing and the custom foam insert protective case stays reproducible at reorder.

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.