Industry Standards Explained for Sealing Thermal & Desiccant

What the Standards Actually Govern — and Where They Diverge #

Buyers sourcing sealing thermal and desiccant materials from China encounter a multi-layered standards landscape that is not well documented in English. The relevant standards span sealing performance (compression set, stress relaxation, leak rate), thermal interface behavior (conductivity, contact resistance, compressibility), and desiccant activity (adsorption capacity, equilibrium moisture content, indicator compliance). Each of these performance domains has its own standard family — and regional variants of those families do not always specify the same test conditions or acceptance thresholds.

The practical consequence is predictable: a supplier declares “ISO compliance” on the COA, ships product that was tested to GB/T conditions, and the buyer’s incoming inspection rejects it because the acceptance limit in the purchase order referenced ISO Standards — specifically ISO 9001 as the quality system and ISO 18472 or equivalent for desiccant performance — without specifying which clause or acceptance class applies.

The gap between declaring a standard and meeting it under the buyer’s test conditions is where most specification disputes originate. This section maps the key standards by sub-category so you can write RFQ requirements that close that gap.

Head-to-Head Comparison — Regional Standards Across Sub-Categories #

The table below covers the three main material groups in this category: elastomeric seals (including thermal gaskets), desiccant materials (silica gel and molecular sieve), and thermal interface materials. For each, it lists the primary international standard, the Chinese national equivalent, the relevant ASTM International method, and the critical difference a buyer needs to know.

Standards comparison current as of H1 2025. GB/T editions are updated periodically — always verify the active edition at SAC China Standards before finalizing RFQ language.

After reviewing this table, the standard selection decision becomes more concrete. For desiccant procurement where the end application is pharmaceutical packaging, the static gravimetric method in ISO Standards ISO 18472 is the specification to cite — not GB/T 10455 — because the test conditions are defined and internationally auditable. The numerical results are not interchangeable; a supplier reporting 28% moisture adsorption per GB/T 10455 dynamic method may deliver material that tests at 22–24% under ISO 18472 static conditions, which can push the product below the 25% minimum adsorption threshold common in pharmaceutical desiccant specifications.

For thermal interface pads, I’d prioritize ASTM International ASTM D5470-17 as the specified test method over GB/T 22588, specifically because D5470 requires the test to be conducted at a defined contact pressure. Chinese suppliers frequently report conductivity values measured at near-zero contact pressure, which can overstate real-world performance by 15–30% in a bonded or clamped assembly. This matters more than most technical buyers realize when they are down-selecting between a 3.0 W/m·K pad and a 4.0 W/m·K pad — the gap on paper may disappear entirely under application conditions.

For elastomeric seals used in static gasket applications with elevated-temperature service, EN 13555:2014 combined with a stress relaxation acceptance criterion (minimum bolt-load retention of 70% after 16 hours at service temperature) is more informative than hardness or tensile data alone. GB/T 12385 at 23°C tells you almost nothing about what happens at 120°C.

The Overlooked Variable — Test Condition Standardization Within the PO #

The comparison table identifies which standard to cite. What it cannot capture is a subtler issue: even within a single standard, test conditions are often left to supplier discretion unless the buyer specifies them explicitly.

Take ASTM D395 Method B for compression set. The standard defines the method but allows the buyer or specifier to select the test temperature and duration from a range of options. A supplier testing at 70°C/22 hours reports a very different compression set value than one testing at 125°C/70 hours — and both are “ASTM D395 compliant.” In our QC-12 incoming inspection protocol, we require that compression set be reported at the actual service temperature of the application, not at the laboratory default. For a seal rated to 120°C continuous service, 70°C/22h compression set data is decoration, not qualification evidence.

The same issue appears in thermal conductivity testing. ASTM D5470-17 specifies a test pressure range of 10–200 psi. A supplier testing at 10 psi and a buyer’s application running at 50 psi will see a measurable gap in real thermal resistance. When we audit supplier test reports, we flag any conductivity data that does not state test pressure. Roughly one-third of the COAs we reviewed in 2024 across thermal pad suppliers omitted this condition entirely.

This is where an RFQ template that says “ASTM D5470 compliant” fails the buyer. The PO needs to say: “Thermal conductivity per ASTM D5470-17, measured at 50 psi contact pressure, minimum 4.0 W/m·K.” That closes the loophole.

A parallel risk exists in desiccant specifications. ASTM International ASTM E104 governs humidity-controlled environments but is not a direct desiccant performance standard. Buyers who cite it expecting a desiccant activity specification are citing the wrong document. The correct approach for pharmaceutical or electronics packaging desiccants is to specify adsorption capacity in grams per unit at defined relative humidity conditions — typically 20% RH and 40% RH — in addition to citing the standard. Units that meet the weight specification but fail the adsorption test at 20% RH are a known failure mode in low-humidity packaging applications.

There is also an active disagreement in the industry about how to handle indicator silica gel. Some buyers specify that color-change indicators must meet EU ECHA REACH SVHC restrictions (specifically the cobalt chloride restriction under Annex XIV), while others accept DMF-free certification as sufficient. These are not equivalent requirements. REACH Annex XIV covers cobalt chloride-based indicators; DMF (dimethyl fumarate) is a separate restriction under REACH Article 67. Our practice is to require both confirmations in writing for any desiccant destined for consumer packaging or pharmaceutical use — but we recognize that for industrial desiccant in sealed equipment enclosures, the regulatory exposure is materially lower, and some procurement teams reasonably choose not to require both.

Implementation Notes — Translating Standards Into Incoming Inspection #

Once you have specified the right standard, test method, conditions, and acceptance class in the PO, the next question is how to verify it at incoming inspection without running a full test lab on every shipment.

For elastomeric seals, the minimum viable incoming check covers Shore A hardness (per ISO 48-4 or ASTM D2240, ±3 Shore A from nominal) and a dimensional check against the drawing tolerance. Full compression set testing per ASTM D395 at service temperature takes 70+ hours and cannot be done on every lot. Our approach: run compression set testing on the first three lots from any new supplier or after any formulation change, then move to hardness-only spot checks at a sampling level of ASTM International AQL 1.0 for critical seals. If hardness drifts more than ±2 Shore A in two consecutive lots, we trigger a full compression set retest before the lot is released.

For desiccant units, the practical incoming check is unit weight per DIN 55473 (±5% tolerance), visual inspection for packaging integrity, and a spot adsorption test on 3–5 units from the lot using a gravimetric method at 40% RH/23°C for 24 hours. A passing result is ≥15% weight gain for Type A silica gel (lower for Type B) — the exact threshold should be agreed with the supplier at the qualification stage and written into the inspection standard.

For thermal interface materials, incoming checks should cover:
– Thickness measurement at five points per sample (tolerance per drawing, typically ±10% of nominal)
– Shore OO hardness as a proxy for compressibility consistency lot-to-lot
– Visual check for delamination, voids, or release liner defects
– Thermal conductivity spot test per ASTM D5470 on one sample per lot for critical applications (full test on qualification lots and after any supplier process change)

The timeline recommendation: complete supplier qualification testing (full standard test suite) before committing to volume. For seals and thermal pads, three consecutive production lots at qualification sample size is the minimum to establish lot-to-lot consistency data. For desiccant, six months of production data across at least four lots is more meaningful — adsorption performance in silica gel can degrade with storage if the supplier’s packaging or warehousing conditions change seasonally. We have seen first-lot qualification pass and fourth-lot incoming fail, specifically in Q3 when Chinese warehouse temperatures rise and improperly sealed bulk packaging allows partial pre-saturation before shipment.

For buyers sourcing o-rings-static-seals or related elastomeric products alongside desiccant, aligning the incoming inspection schedule across both categories reduces overhead without compromising coverage.

Practical Guidance for Buyers #

When sourcing sealing thermal and desiccant materials from China, the first specification to request from a supplier is not the material datasheet — request the test report, specifying which standard edition, which test conditions, and which acceptance class was used. A datasheet that says “per ISO 815” without specifying Part 1 vs. Part 2, test temperature, deflection percentage, and duration is not a qualification document; it is a marketing claim.

The specific risk scenario to anticipate: a supplier qualifies on ASTM D395 Method B at 70°C/22h and ships production lots that have never been tested at your service temperature of 120°C. The Shore A hardness checks pass at incoming, the dimensional checks pass, and the seals fail in service at month 4 because compression set at temperature was never verified. This failure pattern is predictable and preventable if the PO explicitly states the test temperature and duration as a COA requirement.

Before volume commitment, insist on three consecutive production lot COAs that include compression set (at service temperature), Shore A hardness, and dimensional inspection data — not just the qualification sample report. For thermal interface pads, require that conductivity data state the test pressure. For desiccant, require adsorption data at both 20% RH and 40% RH conditions so you can assess performance across the humidity range your packaging actually encounters.

Buyers managing adsorption-desiccant procurement should note that adsorption capacity specifications in Chinese supplier datasheets almost uniformly reference GB/T 10455 dynamic column conditions — not the static gravimetric conditions used in ISO 18472 or pharmaceutical industry practice. Treat those numbers as indicative only until you have independently verified adsorption performance under your specified test conditions.

FAQ

Which standard should I cite in an RFQ for desiccant used in pharmaceutical packaging?
Cite ISO 18472:2006 for adsorption performance, specify the test conditions (static gravimetric, 23°C, 40% RH), and add a separate REACH compliance declaration covering both cobalt chloride (Annex XIV) and DMF (Article 67). GB/T 10455 is not an acceptable substitute because the dynamic column method produces results that are not numerically comparable to ISO 18472 static method output.

Is GB/T compliance sufficient for export products?
It depends on the destination market and application. For industrial MRO seals with no regulatory end-use requirement, GB/T is often adequate. For pharmaceutical, food contact, or CE-marked equipment, GB/T compliance alone will not satisfy the documentation requirements of ECHA REACH, FDA 21 CFR, or EU machinery directive conformity assessments. Specify the relevant regional standard explicitly in the PO rather than accepting GB/T as a default.

Can I use Shore A hardness as the primary incoming inspection criterion for elastomeric seals?
As a routine lot-release screen, yes — with the caveat that hardness checks must be calibrated against at least one compression set verification per the first three production lots. Hardness alone does not catch raw material substitution at the compounder level if the substituted polymer is formulated to the same Shore A target. We flag any Shore A drift of more than ±2 points across consecutive lots as a trigger for full retest, not just rejection of the drifted lot.

What is the difference between EN 13555 and GB/T 12385 for gasket sealing?
EN 13555:2014 requires stress relaxation data at multiple temperatures (50°C, 100°C, 150°C) and uses standardized test fixtures; GB/T 12385-2021 requires only a single temperature condition, typically tested at 23°C. For any gasket application above 80°C service temperature, GB/T 12385 data is not adequate for design validation — request EN 13555 data explicitly.

Do thermal conductivity values on Chinese supplier datasheets typically overstate performance?
Frequently, yes — not because of fraud, but because GB/T 22588 does not mandate a test pressure condition, and suppliers naturally test at low pressure where conductivity reads highest. Values reported at near-zero contact pressure can be 15–30% higher than what you will measure under application clamping pressure per ASTM D5470-17. Always ask for the test pressure alongside the conductivity value, and specify your application pressure in the RFQ so the supplier tests under realistic conditions.

Published by sinoraw.com Technical Team | Request a sourcing consultation