How to Read a T1 Trial Report: EPP and EPS Mold Qualification

Quick answer: A T1 trial report is the first formal evidence that a new EPP or EPS tool can make an acceptable part, and it is the document you should sign against — not just a box of samples that looks right. A usable T1 report records the moulding conditions actually used, the dimensional results against the drawing, part weight and density, fusion quality, the achieved cycle time, cavity-to-cavity consistency, and a clear list of what still needs to change. The most common mistake is approving a tool from appearance alone: bead foam parts look acceptable long before they are dimensionally stable, so the checks that matter are the ones taken after conditioning, not the ones taken off the machine. Agree the acceptance criteria before the trial, and the report becomes a decision document instead of an opinion.

What "T1" actually means in bead foam tooling

In thermoplastic injection moulding the trial sequence is widely standardised. In bead foam it is looser, which is exactly why buyers get caught out. For the purposes of a tooling contract, T1 should mean: the finished tool, mounted on a production-intent machine, moulding the specified bead grade, with the first full set of samples produced and measured. Everything before that — soft tooling, CNC-machined prototypes, single-cavity pre-production tools — is development, not qualification.

That distinction matters because a CNC-machined prototype and a moulded part are not the same thing, even in the same material. A machined sample has no bead structure: its density, skin and impact behaviour differ from the moulded part it is standing in for. If a sample set arrives as machined blocks, ask directly which process made them. Our note on taking an EPP part from concept to production explains where prototype evidence is useful and where it stops being representative.

The trials after T1 are corrective: T2 and beyond exist to close the gaps the first report identified. A tool that needs three rounds is not automatically a bad tool — but a supplier who will not put the T1 gaps in writing is telling you how the rest of the project will go.

Agree the acceptance criteria before the trial, not after

Almost every dispute about a foam tool comes from a criterion that was never written down. The tool makes a part, the buyer expects it to drop-ship a fragile product, nobody agreed the drop height, and the argument happens three months late.

Conditioning: why you should not measure parts off the machine

This is the single biggest technical trap in foam part qualification. A freshly moulded bead foam part still contains moisture and internal gas pressure, and it continues to move for a period after demoulding. Measure it immediately and you record a number that will not match the same part next week — or in your customer's incoming inspection.

Standard practice is to condition samples in a controlled atmosphere before final measurement. ISO 291 defines the standard atmospheres used for conditioning and testing plastics, the most common being 23 °C and 50% relative humidity. Conditioning periods for bead foam parts are typically quoted in the range of 24 to 72 hours depending on part thickness and how wet the moulding was, and thicker sections need longer. Whatever value you choose, the rule that matters is that it is the same value on every report, so results stay comparable across T1, T2 and production audits.

Dimensionally, bead foam should not be specified like an injection-moulded thermoplastic. Typical tolerances for bead foam parts are often expressed in the region of ±0.5–1% of the nominal dimension, and wider across a parting line or where ejector marks and vent witness are unavoidable. Attempting to hold injection-moulding tolerances on a foam part does not improve the part — it inflates tool cost and rework. The right move is to identify the genuinely critical interfaces, tolerance those, and leave the rest general.

Weight and density: the cheapest health check

Weighing parts is fast, non-destructive and far more informative than it looks. Within one cavity and one bead lot, part weight tracks how well the cavity filled and how consistently the beads fused. A spread of weights across a sample set usually points to fill variation; a low average points to under-fusion or short fill; a rising trend across a run often points to a fill gun or vent beginning to block.

Apparent density, when it needs to be stated formally, is normally determined by a standard method rather than by calculation from dimensions — ISO 845 or ASTM D1622 for rigid cellular plastics. That distinction matters because the drawing, the RFQ and the test report should all refer to the same method, otherwise two correct numbers will disagree.

Density is also the variable with the widest performance consequence, which is why it belongs in the acceptance criteria rather than in the toolmaker's notes. See how EPP bead density changes strength and cost for the relationship you are actually specifying when you set a target density.

Fusion quality: judge it by breaking it

A bead foam part with poor internal fusion can look entirely acceptable. The surface is formed against a polished cavity; the weakness is between beads, in the middle of the section. That is why the standard check is destructive: break a part open and look at the fracture surface.

• Good fusion — the fracture runs through the beads. Beads tear rather than separate.
• Poor fusion — the fracture runs between the beads. Whole beads pull out cleanly and the surface looks like loose beads.

Record the result as a ratio rather than a comment — count fused versus unfused beads across the fracture and note where the weak zones sit. Weak fusion is rarely uniform; it concentrates in thick sections, far from fill points, or in areas with poor steam access, and that pattern tells you whether the fix is a process change or a venting change. The symptom catalogue in our EPP and EPS moulding defects guide maps these patterns to their causes.

Cycle time: ask for the sustained number

Every trial report should state the moulding conditions used — steam pressure and time, cross-steam or one-sided steaming, cooling or vacuum time, and stabilisation — and the resulting cycle. What you want is not the fastest shot achieved but the cycle the tool held over a continuous run, because that is the number your capacity plan inherits.

A single fast shot is easy to produce: a hot tool, a short stabilisation hold and a favourable part will all flatter it. A sustained run exposes whether the cooling circuit can really remove the heat and whether the parts are demoulding without distortion once the tool reaches thermal equilibrium.

Cycle time is also the one T1 result that is effectively permanent. Venting density, cooling channel layout and stabilisation capacity are fixed in the metal, so a cycle problem discovered at T1 is cheap to fix and expensive to fix later. The economics of that trade-off are set out in what drives EPP and EPS mould cost — which is precisely why cycle belongs in your acceptance criteria rather than in an appendix.

Cavity-to-cavity consistency on multi-cavity tools

On a single-cavity tool, one good part means the tool works. On a four-cavity tool it means one quarter of the tool works. Each cavity should be sampled, weighed and measured separately, and identified by cavity number — not pooled into one sample bag.

What you are looking for is a consistent pattern: cavity 3 consistently heavy or consistently slightly short tells you about fill or vent imbalance; a cavity whose parts shrink differently tells you about local cooling. Balanced multi-cavity foam tools are genuinely harder to build than single-cavity ones, which is why cavitation decisions should be made against real volume rather than assumed volume.

Functional and transit validation

Dimensional and fusion results qualify the tool. Functional testing qualifies the part. For protective packaging that normally means a drop or transit test against a named standard — ISTA 3A or ASTM D4169 are the common references; for compression-critical parts, ASTM D1621 or ISO 844. Naming the standard at RFQ stage is what prevents a tooling change later, so at T1 the question is simply whether the agreed test was run and whether the results are attached.

Where the part is going into an automotive or regulated supply chain, expect a formal first article inspection as well: a full dimensional report against ballooned drawings, often delivered in an AIAG PPAP or AS9102 FAI format. Ask early which format your customer requires, because it changes what the supplier has to produce and measure at T1 — not just how the results are presented.

What you should receive with the trial report

A T1 package is more than samples. These are the items worth listing as deliverables in the order, because they are far cheaper to include at build time than to request afterwards:

The three honest outcomes of a T1

"Accept with conditions" is where most value is lost or won. It is a legitimate and often sensible outcome — but only when the conditions are specific. An open sentence such as "minor surface marks acceptable" will be read differently by everyone who reads it, including your incoming inspector a year later.

Frequently asked questions

Related reading: what drives EPP and EPS mould cost, how to fix common moulding defects, mould maintenance and storage and how EPP bead density affects strength and cost. Explore our customised EPS/EPP moulds, EPP 20L box mould, EPP and EPS shape moulding machines and EPP materials, or see how we take a part from concept to mass production.