Does case foam replacement always mean a whole new insert?

Answer: Look at the spread. If 3 of 5 points sit inside 15%, replace only the loaded layer and the cost drops from 38 to 16; beyond 3 failing points a patch will not last 3 months.

Is the 3 s press reliable?

Answer: It works as a screen, since a dent at 5 min almost always means set is out of spec. For a report, still run 25% compression for 24 h, and expect both methods to agree except near the limit.

Must yellowed foam be replaced?

Answer: No. Yellowing on EVA is antioxidant bloom and says nothing about load bearing; recovery, set and collapse are the real measures. Yellow plus crumbly is ageing.

Is 24 months a hard limit?

Answer: It is a planning baseline, not a scrap date. Dry sites can run to 30 months with a set check every 6 months, while humid coastal sites schedule at 18.

Case Foam Replacement: When Foam Needs Replacing

Q: Can old inserts be sold?

Answer: Clean EVA cut foam goes for about 3 per 1.2 kg set, while adhesive or flocked foam has no recovery value and leaves as general waste. Mixed loads get rejected wholesale.

Quick answer: Case foam replacement hinges on one test: press 3 s, and if the dent lasts 5 min with set above 15%, the insert is spent. Replace it.

The first test: 3 s press and 15% set
Checking the EVA 45 kg/m³ baseline
Measuring 2 mm wall collapse
Mould, odour and the 24-month cycle
Post-fit checks and old foam recovery
FAQ

1. The first test: 3 s press and 15% set

Foam that still looks fine may already have stopped working. Press a thumb into the most loaded spot for 3 s and let go: a surface that comes back within 5 s still has life, a dent still visible at 5 min means it has lost the argument.

Numbers settle a case foam replacement decision. Cut a 10 mm sample, compress it to 25% of thickness, leave it 24 h, release and measure after 30 min: above 7.5 mm means set is inside 15%, below that the fit is over.

Why 15% and not 25%? Foam must hold 0.5 mm to 1 mm of interference between load and wall. Set eats 15% of the thickness, that interference disappears and the load floats 3 mm, hitting foam, then wall, then floor.

Sampling position beats caliper precision. The loaded zone dishes, so a centre-only reading overstates ageing; take 5 points across centre and corners, and a point 1 mm off the mean means the sheet was cut unevenly.

Criterion	Tool	Fail line	Recheck
Recovery	Thumb, 3 s	Dent at 5 min	Monthly
Compression set	0.02 mm caliper, 5 points	Above 15%	12 months
Thickness	Caliper vs original	One point 1 mm low	With set test
Collapse	Depth gauge	Above 2 mm	6 months
Mould	Eye, torch	3 spots over 5 mm	Monthly, humid season

2. Checking the EVA 45 kg/m³ baseline

The nominal density of EVA inserts here is 45 kg/m³, and that number decides whether the sheet survives 40 kg of equipment and a 1.2 m drop. Verifying it is crude work: cut 100 mm × 100 mm × 50 mm, which is 500 cm³, expect 22.5 g, and accept 21.4 g to 23.6 g, a ±5% window, on a 0.1 g scale.

Density 10% under baseline means thinner cell walls and collapse within 3 months; 10% over means slower recovery and worse shock absorption. If a new insert for a case foam replacement weighs 19 g instead of 22.5 g, ask which batch it came from.

Case foam replacement survey in a lit tent, three olive cases used as a bench under maps, radios and headsets, stencilled numbers on the sides

Sample	Volume	Expected	Acceptable
100 × 100 × 50 mm	500 cm³	22.5 g	21.4–23.6 g
50 × 50 × 50 mm	125 cm³	5.6 g	5.3–5.9 g
100 × 100 × 50 mm	500 cm³	19.0 g	Reject, near 38 kg/m³

Density inside one batch should stay within ±3%. A spread above 1.5 g across three samples means regrind, whose cells age about twice as fast as virgin sheet, and the check takes 10 min against three months of rework.

3. Measuring 2 mm wall collapse

Collapse is about the walls, not the floor. Lay a steel rule across the cavity mouth as a bridge, drop a depth gauge vertically to the deepest point of the wall, and subtract from the original depth: anything over 2 mm is collapse. Read 4 corners and the centre of every cavity, and the deepest point decides.

The consequence is loss of grip. With wall squareness off by 0.5 mm the load shifts 3 mm sideways and transport vibration turns into impact, while the foam surface still looks untouched, which is why case foam replacement cannot run on appearance.

Collapse has three sources: long compression, moisture uptake then shrinkage, and cut-edge fatigue. EVA held at 40 ℃ and 80% RH for 72 h takes up about 8% of its mass in water and never returns to full thickness, and a batch that waited three weeks at a wet-season dock came back 2.5 mm shallow.

Record direction too. Collapse at the handle side means one-sided carrying, even collapse at four corners is the load's weight, and a single bad cell means an oversized item has been pushing the wall out.

Chart it as you go: sketch a plan view, write the readings in place and remeasure in three months. Anything above 1 mm of collapse per 6 months means the cavity was oversized.

4. Mould, odour and the 24-month cycle

Mould is the one criterion never to postpone. Three grey-green spots over 5 mm, or a sour smell within 10 s of opening, means the insert is saturated, and wiping will not fix hyphae grown into the open cells.

Environment sets the cycle. A dry shop opening twice a day schedules case foam replacement at 24 months; coastal sites and shipping move to 18; cold storage inspects at 12.

Case foam replacement result in a black open case, three square lid pockets, a round cable recess and a meter slot in the base foam

The clock starts at first wetting, not at the production date: from one batch, cases in a conditioned store lasted 5 years while cases under an open shed failed in 2, so log both dates.

Grade the smell. A faint adhesive note clears within 7 days; a sharp sour or musty smell means anaerobic growth, and that case needs 48 h open before new foam goes in.

Storage can stretch the interval. Leave the case open when empty, since a closed lid keeps the foam under load and set accumulates while it sits idle; hold the store under 60% RH so EVA takes up moisture half as fast. Stacked against an outside wall, the reverse happens and mould starts on the hidden back face.

5. Post-fit checks and old foam recovery

Measure before latching. Cavities should leave 0.5 mm to 1 mm to the item outline and 2 mm of compression in depth. Lid closed, the seam stays under 1 mm and a thumb on the centre sinks no more than 1 mm.

Material cost runs about 38 per set, one 30 mm cut sheet plus a 10 mm pad, and refitting takes 40 min for strip-out, cleaning, fitting and checking. Labour is more than half the cost, so one correct case foam replacement beats two experiments.

Old inserts split two ways. Clean EVA offcuts hot-press into pallet blocks at roughly 3 per 1.2 kg set, while adhesive or flocked foam has no recovery value and leaves as general waste. Shake the crumbs out first.

Condition	Action	Interval	Cost
Set under 10%	Keep, check	6 months	0
Set 10–15%	Patch or shim	3 months	6
Set above 15% or 2 mm collapse	Replace	Now	38
Mould or odour	Replace, air 48 h	Now	38 plus 2 h
Squareness over 0.5 mm	Replace, remeasure	Now	38 plus 30 min

Conclusion

Case foam replacement runs off one table: keep the insert while set stays under 10%, patch between 10% and 15% and recheck in 3 months, replace the sheet above 15% or at 2 mm of wall collapse, replace and air the case for 48 h at three or more mould spots, and remeasure the cavity when wall squareness passes 0.5 mm. Start the clock at first wetting, then plan 24 months in dry shops, 18 on the coast and 12 in cold storage, since at 38 per set plus 40 min of labour a second attempt always costs more.

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