Is higher density always better for a custom foam insert case?

Answer: No. It resists sinking, but at equal thickness it is heavier and over-compresses light units. Above 70 kg/m³ interiors only gain mass.

Is a ±1 mm cutting tolerance enough?

Answer: For pocket length and width, yes. Depth is tighter, so give it ±1.5 mm from the pocket floor.

Does a higher layer count fit the product better?

Answer: No. Layers serve changeover, letting one layer be replaced whole at the cost of 0.1 mm deviation and a hard spot.

Which pages of a flame and RoHS report matter?

Answer: The method and afterflame time behind the burning class, the ten RoHS substances split, and whether the grade matches this lot.

Custom foam insert case specs: 25-70 kg/m³, Shore A, ±1 mm

Quick answer: A custom foam insert case is specified by six measurable numbers: density, hardness, cutting tolerance, die clearance, layer count and compression set. Fix density and hardness from unit weight and contact area, hold pockets with a ±1 mm tolerance, then close with 5% compression set plus flame and RoHS reports.

The Six Parameters of a Custom Foam Insert Case
Density and Hardness Are Separate Decisions
Cutting Tolerance and Die Clearance
Layer Count From One to Four
The Five Percent Compression Set
Flame Retardance and RoHS
FAQ

1. The Six Parameters of a Custom Foam Insert Case

An insert specification is not negotiated by feel. Six parameters can be drawn and re-checked: density, hardness, cutting tolerance, die clearance, layer count and compression set. Soft, springy and snug must each become one of those six.

Order runs weight, contact area, allowed sink, then density and hardness, then layer split, then tolerance. Table 1 is read by unit weight, not case size.

Material	Density (kg/m³)	Hardness (Shore A)	Working load (kg)
Low density EPE	25-35	25-35	0.5-3
Medium density EPE	40-55	35-45	3-8
EVA	45-70	40-60	8-20
PU	30-60	25-50	2-12

A 2.4 kg rangefinder on four 25 mm pads gives 2500 mm² of contact at 0.009 MPa; 30 kg/m³ EPE sinks 2 mm, 55 kg/m³ stays under 0.8 mm.

2. Density and Hardness Are Separate Decisions

Writing density and hardness as one number is why a custom foam insert case arrives feeling wrong. Density governs sinking under load and repeated compression; hardness governs contact pressure and finish marking. The same 45 kg/m³ block sits at 30 or 50 Shore A.

Custom foam insert case: black shell open on a grey floor, foam blocks in lid and base with stepped and square pockets, two latches

At 0.005 MPa, 25 kg/m³ EPE sinks 8%, 45 kg/m³ 3%, 70 kg/m³ EVA 1.5%. Density moves capacity in multiples; hardness trims within a band.

Optics take 25-30 Shore A, where a deeper sink beats a pressure mark. Edged metal takes 45-60 Shore A with a 2 mm relief opposite each edge. Above 8 kg per unit, stay above 40 Shore A or the pocket wall collapses.

3. Cutting Tolerance and Die Clearance

Tolerance placement decides who proves what. CNC reciprocating cutting holds ±1 mm over a 300 mm stroke; past 600 mm the middle drifts about 0.5 mm from wire tension.

Six lines cover the block:

Outer profile: ±1.0 mm from the cavity minus edge allowance
Pocket length and width: ±1.0 mm at the narrowest point
Pocket depth: ±1.5 mm including adhesive build-up
Pocket centre distance: ±1.2 mm from the datum pocket
Wall between pockets: not under 8 mm, or the foam slumps
Die clearance per side: 0.5 mm, down to 0.3 mm below 20 mm

Die cutting differs. A steel rule severs the foam, so clearance controls the edge: too much and the cut sheds crumbs, too little and the foam springs back 0.6 mm small.

4. Layer Count From One to Four

A custom foam insert case uses one to four layers, following the changeover plan rather than pocket depth. What decides it is whether depth exceeds one stable block, whether a middle layer swaps by variant, and whether the lid needs compression.

Custom foam insert case: two black cases on a wooden bench, one closed with its latch, one open showing square and bar foam pockets, screws

One layer suits 20-30 mm pockets at the lowest cost. Two layers, 20+20 or 30+30, carry load below and profile above. Three cover 50-70 mm with a 20 mm base, 30 mm pocket layer and 10 mm facing. Four appear only where a whole layer is replaced.

Keep glue lines under 0.1 mm. A thicker line makes a hard spot that shows up first in a 1 m six-face drop.

5. The Five Percent Compression Set

Compression set is the only parameter that worsens with time, and the one most often skipped. Compress a sample to 50% of its thickness, hold 24 h at temperature, rest 30 min, measure the loss. GB/T 6669 asks 5% or less at 23 °C and 8% or less at 70 °C. Read both: a grade that passes cold and fails hot thins visibly after two weeks in a summer cabin. The loss does not break the case, it loosens the pocket, where 1.5 mm of interference per side falls to 0.4 mm at 8% set, the unit shifts and its edges strike the wall. Design interference from the hot figure.

6. Flame Retardance and RoHS

The insert is the only part using a large volume of expanded material, so flame and hazardous substance reports belong to the insert, not the case body.

Item	Criterion	Test condition
Burning behaviour	GB 8624 class B1	30 s horizontal burn, 0 s afterflame
Oxygen index	26% minimum	GB/T 2406.2
Heavy metals	Pb, Cd, Hg, Cr(VI) each under 100 mg/kg	RoHS homogeneous split
Phthalates	Four items each under 0.1%	RoHS 2.0 amendment
PAHs	Benzo[a]pyrene under 1 mg/kg	AfPS GS 2019 method

Retardants cost resilience: a B1 grade runs 1-2 points higher in compression set, so specify against retardant data.

Conclusion

The insert side of a custom foam insert case reduces to six lines: density, hardness, cutting tolerance, die clearance, layer count and compression set. Keep flame and RoHS on a separate report for the foam. Put those lines on the drawing and a custom foam insert case is accepted against a shared ruler.

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.