VCI Packaging: The Four Jar Tests and the Scales That Disagree

Buyers treat VCI like any other material. Pick a paper or a film, wrap the part, and trust the chemistry to do what the datasheet says.

The datasheet is harder to read than that. A VCI claim rests on a jar test, four countries write their own version of that test, and the versions do not score the same way.

Two plain numbers go missing as well. How much one sheet covers, and how close it must sit to the metal, are the first things a buyer asks. Nobody prints either.

This reference covers what the chemistry does and how the four tests differ. It then covers the scale trap, what one public spec does pin down, and the two figures you have to ask for.

What VCI Actually Does

The chemistry does not stay where you put it. It leaves the paper or film, drifts through the air in the package, and lands as a thin film on bare metal.

That film is what interrupts corrosion, and it reaches places a brush cannot, which is why the method suits assemblies with hollow interiors.

Moving as a vapor comes with a catch. The vapor has to stay concentrated enough to keep working, so it needs a fairly closed space.

So the enclosure counts as part of the specification. A VCI sheet laid in an open crate does very little, because the useful part simply drifts away.

Carrier choice matters for a second reason. VCI paper is paper, bought by corrugated basis weight like any other grade, and that choice has knock-on effects later.

Four Official Tests for One Property

Claims come from a jar test, in which a polished metal panel sits near the VCI material in a sealed jar while damp air does its work. Four separate bodies publish their own version of that test.

Method	Body	Conditioning	A higher grade means
MIL-STD-3010C, Method 4031	US Department of Defense	20 h, 75 °F, 90% RH, glycerin	More rust
NACE TM0208	NACE	20 h damp, plus a heating step	Better protection
TL 8135-0002	German buying office	20 h dry, then 22 °C and 40 °C	Better protection
JIS Z 1542	Japanese Standards Association	20 h at 90% RH, then condensation	Staged, read the scale

They agree on the broad shape and split on the detail, since all four condition for twenty hours and almost everything else moves between them.

They prep the metal differently first. The US method polishes at 240 grit then 400, while the German and Japanese ones use 320 grit, and NACE permits polishing by hand or by machine.

Cleaning splits too, because NACE calls for boiling mineral spirits followed by alcohol rinses, and how a panel starts out is part of how it ends up.

Then the damp-air plans part ways. The US method adds 10 millilitres of 26 percent glycerin and produces condensation with cold water in a hollow tube, then runs three hours more.

NACE adds a heat step after the damp conditioning. That lifts humidity and brings condensation on faster.

The German method runs dry for its twenty hours before glycerin goes in. It then warms for two hours at 22 degrees and two more at 40, with no condensation stage at all.

Only the German method uses that dry-then-humid sequence. The Japanese one takes a third route, holding 90 percent humidity for twenty hours and then producing condensation from cold water, with no heat step.

Laboratories have noticed the gap that leaves. One published variant adds a condensation stage to the German method, replacing the water every fifteen minutes throughout the forty-degree phase. That makes its result less comparable to the standard it came from, rather than more comparable to the other three.

The source that sets them side by side is blunt about the upshot. It says the methods differ in details that can sway results, that each one builds a different corrosion environment, and that the spread makes results hard to compare across standards.

The Scales Point Opposite Ways

Here is where a reporting detail turns into a purchasing risk.

The US method grades under 10 times magnification, and a higher number means more corrosion spots. NACE and the German method both grade 0 to 4, and there a higher number means better protection.

So the same digit flips. A 4 is close to a fail on one report and close to ideal on another, and nothing in the digit tells you which.

The Japanese method does not settle it either. It grades in stages, using percent of area for the low grades and spot counts under a lens for the high ones.

All of which gives you one short question for any claim. Ask which method gave the grade, because without it the number is a digit rather than a result. The direction of its scale cannot be inferred from the figure alone.

Ask how hard the test was, too. The same comparison calls NACE the method that favors chemistry carried by water vapor. It rates the US and Japanese methods slightly less aggressive, and the German one typically the least aggressive of the four.

What a Public Spec Does Pin Down

Some of this is settled, because a United States military specification for VCI-treated paper sets real requirements, and they ask rather more than a datasheet suggests.

Several of them are pass or fail by eye. Copper in the vapor must show no pits, etching or change of color, and a polished steel panel must show no corrosion, etching or pits.

Each criterion carries a named method behind it, which is what makes the specification auditable. The vapor inhibitor check runs under Federal Standard 101 Method 4031 Procedure B, and contact corrosivity under Method 3005. Blocking resistance runs under Method 3003 Procedure A, and the tear figure under ASTM D689.

Two further requirements are easy to overlook. Markings have to stay clear and legible after two hours in a circulating water bath. The paper must also prove compatible with the MIL-PRF-131 barrier material it gets sealed inside.

One of those runs twice, since the same vapor test repeats after exhaustion, so the paper has to work and then keep working once the easily available chemistry has gone.

Touch gets its own test, on carbon steel panels read after twenty hours. Paper that protects by vapor can still mark the metal it rests on, and the specification separates the two questions.

The vapor test also shows that the method discriminates. Treated panels in that paper came out at zero percent corrosion, while the untreated controls ran at roughly 40 percent on the first pass. After exhaustion the controls reached about 62 percent, so the jar measures something real rather than flattering everything placed in it.

The duration requirement is the one worth knowing. Long-term protection asks for no corrosion of steel panels over one year, across four panels.

The paper also has to survive being handled. Burst strength is listed at 40 psi and tear strength at 40 grams-force each way.

One more clause sits beside those. The paper must not harm the barrier bag it gets sealed inside, and that clause matters more than it reads.

A VCI layer that spoils the seal on its own bag has defeated the package. It is the same logic behind treating ESD packaging and moisture barrier as two separate specifications rather than one product.

The Two Numbers Nobody Publishes

Two figures remain unpublished, and they are the two any specification needs most.

The first is coverage, and no source reached states how much volume or surface a single sheet protects, so a package cannot be sized from published data.

The second is separation. Published test rigs suspend the material near the panel without touching it, which establishes that contact is unnecessary and nothing at all about how far is too far.

Treat both as promises the supplier makes, not as facts you look up. Ask for the coverage rate and the maximum separation in writing, against the enclosure you will actually use.

That is the same logic as a tested configuration rather than a material earning approval under UN certified packaging, where what was proven is precisely what you have.

The carrier brings one last knock-on. A paper VCI sheet sealed in a barrier bag carries far more moisture demand than a synthetic insert would, so the desiccant calculation shifts when the corrosion layer does.

Which is the entire specification in one line. Name the method behind the grade, read the scale the right way round, and get coverage and gap committed for your own enclosure.

Common Questions