For a case custom insert, which property decides between EVA and EPE?

Answer: Compression cycles come first. Above 3 kg part weight and 200 loadings a year, EVA at 60 kg/m³ keeps 95% after 500 cycles, while EPE at 25 kg/m³ suits under 50 cycles and saves 26 CNY.

How much does 30 mm cost over 20 mm?

Answer: The thicker version uses 50% more material and moves a set from 68 to 89 CNY. Above 8 kg and an 800 mm drop that step cannot go, or the 21 CNY saved returns as a 260 CNY rework.

What do closed cells do for a case custom insert?

Answer: XPE at 33 kg/m³ keeps over 90% closed cells and under 1% water uptake, so recovery barely moves after 24 h of soaking, while EPE climbs from 4% to 9% compression set once damp.

Is a ±0.5 mm cut good enough?

Answer: It matches 0.4 to 0.6 mm of interference. Die cutting holds ±0.5 mm, which with ±0.2 mm part tolerance lands compression at 20% to 30% and grip near 12 N.

Does a small batch of case custom insert need a mould?

Answer: No. Under 300 sets, die cutting plus lamination costs 800 to 1500 CNY up front, a 3 to 20 piece run is routed at 200 to 400 CNY a set, and a tool is reserved for volume.

Case Custom Insert: EVA, EPE, XPE

Quick answer: For the same 6 kg bench instrument, a case custom insert in EVA at 60 kg/m³ quotes 68 CNY a set against 42 CNY in EPE at 25 kg/m³, so the 26 CNY gap buys compression cycles.

Where the 26 CNY gap comes from
Reading density across three foams
Thickness from 20 to 40 mm
Compression and cut tolerance
Cut die versus mould
Mixing two materials in one insert
FAQ

1. Where the 26 CNY gap comes from

A 6 kg instrument in a 480 mm × 360 mm × 190 mm case drew three insert quotes: 68 CNY in EVA at 60 kg/m³, 55 CNY in XPE at 33 and 42 CNY in EPE at 25.

The 26 CNY buys recovery after compression: EPE cycled 200 times at 25% keeps 88% of its thickness, EVA keeps 95% after 500 cycles, XPE holds 93% after 400 with water uptake under 1%.

One cost never reaches the material line: EPE needs 30 mm to match EVA at 20 mm, uses 50% more volume, and 42 CNY becomes about 51 CNY.

XPE is usually skipped, yet its closed cells hold recovery at 80% humidity or after a wash line. Selection runs environment first, part weight second, price last.

2. Reading density across three foams

Density is the one property that goes straight onto a drawing, and the one quotations blur most: 45 against 60 kg/m³ differs by 33% in material and 12 CNY a set.

case custom insert with segmented cavities, an open olive case on a bench, egg crate foam in the lid and paper bags in the base

Foam	Density (kg/m³)	Cells	Kept after cycling	Price (CNY)
EVA	45 or 60	Partly open	95% / 500	68
EPE	25	Thin walls	88% / 200	42
XPE	33	90% closed	93% / 400	55

EVA 45 suits parts below 3 kg and EVA 60 those above, where cavity walls must stay upright; a 30 mm pocket in the 45 grade dents under a fingernail and frays within 20 loadings.

EPE at 25 expands about 40 times and works for shallow pockets and dividers, collapsing past 40 mm of depth; its price and heat sealing keep short-haul returnable inserts on it.

XPE at 33 is crosslinked with isolated cells and a fine cut face, close to EVA 45 in hardness but steadier in damp sites.

A 100 mm × 100 mm × 20 mm coupon should weigh 12 g at 60 grade and 5 g at 25, and 8% off means the wrong grade arrived.

3. Thickness from 20 to 40 mm

Thickness converts from part weight and drop height. At 800 mm onto concrete with static stress between 0.8 and 1.2 kPa, EVA 60 absorbs about 4 kg per 10 mm, so 20 mm covers 8 kg and 40 mm covers 16 kg.

A 6 kg part given 40 mm wastes 22 CNY, while a 14 kg part given 20 mm dents after three drops and costs more to rework than three sets of thicker foam.

Part (kg)	EVA 60	Price (CNY)	800 mm drop
8	20 mm	68	No dent
12	30 mm	89	No dent
16	40 mm	112	0.2 mm print

Stocked sheet runs 20, 30 and 40 mm in 5 mm steps, and a 25 mm pocket bonded from two sheets creeps 0.3 mm in 12 months.

Ten millimetres in the lid preloads the part 2 to 3 mm, while a 30 mm lid adds 35 N at each latch.

4. Compression and cut tolerance

Grip comes from interference. A cavity 0.4 to 0.6 mm narrower than the part compresses the foam 25% for about 12 N and holds through a 1.2 m drop; under 10% the part rattles, over 40% it must be pulled out.

case custom insert comparison, two open grey cases on a wood shelf, left foam cut around spanners, right foam with two long slots

Part tolerance of ±0.2 mm plus cut tolerance of ±0.5 mm swings real interference between 0.2 and 0.8 mm, which keeps compression in the 20% to 30% band and grip within 4 N.

Routing, die cutting and hot pressing hold ±0.3, ±0.5 and ±1.0 mm: the knife suits sheet under 20 mm, the die straight cavities to 40 mm, the press curved or stepped ones.

In a 40 mm pocket, 0.5 mm of edge offset jams the part at 30 mm of travel, and a two-sided knife path holds verticality at 0.3 mm where one pass drifts past 1 mm.

5. Cut die versus mould

A steel-rule die is an 18 mm plywood board with a knife line that stamps a 2D outline for 800 to 1500 CNY in 3 days, cutting only through-slots whose walls sit square to the face.

An aluminium tool for hot pressing costs 6000 to 12000 CNY over 12 days and produces curved pockets with draft, stepped cavities and shaped edges, the walls carrying 3° so parts settle themselves.

Item	Steel-rule die	Aluminium tool
One-off	800–1500 CNY	6000–12000 CNY
Lead time	3 days	12 days
Shapes	Through-slots	Curves, steps
Accuracy	±0.5 mm	±1.0 mm
Batch	Under 300	Over 300

The 300 set line is amortisation: 9000 CNY of tooling spread over 30 CNY a set breaks even there, below which lamination wins, above which moulding undercuts it.

CNC routing fills the gap, milling 3 to 20 prototypes at 200 to 400 CNY a set, where a change only edits the program.

6. Mixing two materials in one insert

One material rarely fills a whole insert. A 30 mm EVA 60 base, a 10 mm EPE 25 lid layer and 15 mm XPE 33 side strips cost 18% less than an all-EVA build.

Bonding is the hard part. Foam adhesive needs 8 N/25 mm of peel, the EVA to EPE interface drops to 5 N/25 mm, so corona treatment comes first.

Compartments mix as well: 60 grade in heavy zones, 45 in light ones, 3 mm PVC dividers between layers, which saves 25% of material.

Each layer then does one job, and insert life runs from 12 months to 30.

Conclusion

The three foams are not ranked, they are assigned. For an instrument case around 3 kg that opens daily, a case custom insert in EVA at 60 kg/m³ with a 20 mm base and a 10 mm lid layer costs 68 CNY and survives 500 cycles; for short-haul transport on a budget, EPE at 25 kg/m³ costs 42 CNY and 30 mm restores the cushioning; for cold stores and seaside warehouses, XPE at 33 kg/m³ costs 55 CNY and closed cells outweigh the 13 CNY saved. Read thickness off part weight, hold interference at 0.4 to 0.6 mm, compress 25% and grip at 12 N, then die cut below 300 sets and mould above.

Foam	Density	Part weight	Thickness	Price	Note
EVA	45 or 60	Over 3 kg uses 60	20 / 30 / 40 mm	68	Walls must stand
EPE	25	Under 3 kg	30 mm	42	Cost first
XPE	33	3–12 kg, damp	15 / 20 mm	55	Closed cells

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.