What GB/T 8939 Actually Tests in a Sanitary Pad (and What the 2025 Update Changes)

Every sanitary pad sold in China has to answer to GB/T 8939 in one way or another. It's the national standard for pads and panty liners, and it's been the industry referee since 2018. If you've ever wondered what "absorbency" or "pH" actually means on a spec sheet, this is the document that defines it.

I'm going to walk through the current version, GB/T 8939-2018, because that's what factories are still certifying against today. There is a 2025 revision coming into force on January 1, 2027, and I'll flag the biggest changes at the end so you know what's shifting.

The metrics that matter

The standard checks three things: physical dimensions, how the pad performs when wet, and what it's allowed to contain.

Physical dimensions

• Full-length deviation: ±4% of the labeled length. So a 240 mm pad can be 230–250 mm and still pass.
• Strip mass deviation: ±12%. This checks that the absorbent core isn't wildly inconsistent from one pad to the next.

These sound boring, but they catch the "shrinking pad" problem that blew up on social media in late 2024. The 2025 revision tightens the length rule to a lower deviation of no more than -2.0%, mostly to protect buyers from pads that quietly get shorter.

Performance

• Absorbency ratio (吸水倍率): ≥7.0 for pads. The test soaks the whole pad for 60 seconds and measures how much liquid it holds relative to its dry weight. It's a capacity test, not a speed test.
• Absorption speed: ≤60 seconds. This replaced the old "penetration amount" test because the new method uses a curved fixture that acts more like a human body. Speed and capacity are not the same thing.
• Back-adhesive peel strength: 100–800 mN. Too weak and the pad slides around. Too strong and you risk residue on underwear. We've written about why back-adhesive residue happens and how factories control it.

Safety

• pH: 4.0–9.0 in the 2018 version.
• Formaldehyde: ≤75 mg/kg.
• Migratable fluorescent agents: Pass (no strong fluorescence).
• Microbiology: Governed by GB 15979, which caps bacteria and fungi and bans pathogens.

The microbiology part is non-negotiable. A pad can have fancy packaging and still fail if the production environment or raw materials introduce contamination. That's why the standard also bans recycled raw materials and requires each pad to be individually wrapped.

What's changing in GB/T 8939-2025

The 2025 revision raises the bar in a few ways. The biggest shifts:

• Length deviation: Lower bound tightened to ≥-2.0%.
• Mass deviation: Tightened to ±10%.
• Absorption speed: Dropped to ≤50 seconds for pads 200 mm and longer.
• Rewet amount: New cap of ≤3.0 g, so a pad can't just absorb fast and then leak wetness back to the skin.
• pH: Narrowed to 4.0–7.5, closer to skin's natural acidity, which is why sensitive-skin users should watch the pH line.
• Formaldehyde: Cut to ≤6.0 mg/kg.
• New chemical limits: Added phthalates, heavy metals (lead, arsenic, cadmium, mercury), and disallowed aromatic amine dyes.
• Fluorescent agents: Changed from "pass" to "not detected."

It doesn't take effect until 2027, and products made under the 2018 standard can still be sold until then. But if you're planning a private-label line, designing to the 2025 limits now is the safer bet.

FAQ

Does GB/T 8939 apply to period pants?

No. Pant-style products have their own standard, GB/T 39391-2020. Some older packs still quote GB/T 8939, but for true pant construction, 39391 is the correct reference. Read our explanation of GB/T 39391 here.

Is a higher absorbency ratio always better?

Not really. The standard only requires ≥7.0. A pad that holds 20× its weight isn't necessarily more comfortable, and for daytime use it can become overkill. We explain the absorbency-number paradox here.

What's the difference between absorption speed and absorbency ratio?

Speed is how fast the surface dries after a dose of liquid. Absorbency ratio is total capacity after soaking. A pad can be fast but small, or huge but slow. Good design balances both.

Should I worry about formaldehyde in pads?

At compliant levels, no. The 75 mg/kg limit is conservative, and the upcoming 2025 standard will drop it to 6 mg/kg. If a factory can't show a test report, that's a red flag, not the number itself.

How do I check if a supplier really tests to GB/T 8939?

Ask for the test report number and the lab. Check that the report covers the exact SKU, not just a "similar" product. If you're comparing OEM factories, ask whether they run incoming QC on fluff pulp and SAP, because raw-material control is where most failures start.

Note: This article reflects GB/T 8939-2018, the version currently in force, and previews GB/T 8939-2025 as a future benchmark. Always confirm the effective version before finalizing compliance claims.