Not all stainless steel is the same. The cup in your hand could be SUS304 (food-grade, corrosion-resistant, safe for daily use) or SUS201 (cheaper, less corrosion-resistant, and a potential health concern for long-term food contact). From the outside, they look identical. The difference is in the alloy composition — and it matters for your health.
This guide explains what SUS304 stainless steel is, why it is the safest choice for drinkware, how it compares to other grades, and how buyers can verify they are getting genuine 304 grade rather than a cheaper substitute.
1. What Is SUS304 Stainless Steel?
SUS304 is the Japanese Industrial Standard (JIS) designation for the world's most widely used stainless steel alloy. It is also known as:
AISI 304 — American designation (most common in US specifications)
18/8 stainless steel — Industry shorthand referring to 18% chromium, 8% nickel
EN 1.4301 — European designation
GB/T 06Cr19Ni10 — Chinese national standard designation
The key composition of SUS304:
| Element | Content | Purpose |
|---|
| Chromium (Cr) | 18–20% | Forms chromium oxide layer that prevents corrosion and rust |
| Nickel (Ni) | 8–10.5% | Enhances corrosion resistance and provides a smooth, polishable surface |
| Carbon (C) | ≤0.08% | Low carbon prevents intergranular corrosion during welding |
| Manganese (Mn) | ≤2% | Improves strength and workability |
| Iron (Fe) | Balance (~67–72%) | Base metal |
This combination makes SUS304 highly resistant to corrosion from water, coffee, tea, juice, wine, and all common beverages — which is why it is the global standard for food-contact stainless steel.
2. 304 vs 201 vs 430: Why Grade Matters
The most critical comparison for drinkware buyers is between the three grades commonly used in cup manufacturing:
| Property | SUS304 (18/8) | SUS201 | SUS430 |
|---|
| Nickel content | 8–10.5% | 1–5.5% | 0% (nickel-free) |
| Chromium content | 18–20% | 16–18% | 16–18% |
| Corrosion resistance | Excellent — resists coffee, wine, juice, salt | Moderate — prone to rust in acidic or salty environments | Good for dry environments; poor with acidic liquids |
| Food safety | FDA / LFGB approved for food contact | May leach manganese; not recommended for prolonged food contact | Limited food-contact applications; not ideal for liquids |
| Magnetic? | Slightly magnetic or non-magnetic | Slightly magnetic | Strongly magnetic |
| Cost | Standard (baseline) | 20–30% cheaper than 304 | 15–25% cheaper than 304 |
| Common use | Cups, tumblers, bowls, cookware, medical | Cheap drinkware, industrial applications | Appliance panels, automotive trim, non-liquid food contact |
Warning: SUS201 is frequently substituted for SUS304 in low-cost drinkware because they look identical. The price difference is only USD 0.30–0.80 per cup, but the food safety difference is significant. SUS201 has higher manganese content (5.5–7.5% vs ≤2% in 304), and manganese can leach into acidic beverages. Always verify the grade.
3. 18/8 vs 18/10: Understanding the Difference
Consumers often see "18/8" and "18/10" on product labels and wonder which is better:
| Grade | Designation | Nickel | Practical Difference for Cups |
|---|
| 18/8 | SUS304 / AISI 304 | 8% | Industry standard for drinkware; excellent for all beverages |
| 18/10 | SUS316 / AISI 316 | 10% | Slightly better resistance to salt/acid; premium cutlery grade |
For drinkware, the difference between 18/8 and 18/10 is negligible in practice. Both are fully food-safe and corrosion-resistant for all common beverages. 18/10 (SUS316) commands a 15–25% price premium that is justified for marine environments, surgical instruments, and chemical processing — but not for cups and tumblers.
4. How to Verify Your Cup Is Genuine 304 Grade
There are several methods to verify stainless steel grade, ranging from simple consumer tests to laboratory analysis:
1. Request the Mill Test Certificate (MTC): This is the most reliable method. Every batch of stainless steel from a steel mill comes with an MTC that certifies the alloy composition. Any legitimate manufacturer will provide this on request.
2. Request LFGB or FDA test report: These third-party lab reports test metal migration from the finished product into food simulants. They confirm not just the grade but the finished product's safety.
3. Magnet test (indicative, not definitive): SUS304 is weakly magnetic or non-magnetic. SUS201 is slightly magnetic. SUS430 is strongly magnetic. A strong magnet sticking firmly to the cup suggests it is not 304 — but cold-worked 304 can show mild magnetism, so this test is indicative rather than conclusive.
4. Acid spot test (professional): Specialized stainless steel testing solutions change color based on the nickel content of the alloy. These kits are available from industrial supply companies and cost USD 15–30.
5. Health Concerns Addressed
Common health questions about stainless steel cups, answered with evidence:
| Concern | Answer |
|---|
| Does stainless steel leach into drinks? | SUS304 shows negligible metal migration in FDA and LFGB testing — well below safety thresholds for chromium and nickel. It is classified as safe for repeated food contact. |
| Is stainless steel BPA-free? | Yes. BPA (bisphenol A) is a plasticizer found in polycarbonate plastic and epoxy resins. Stainless steel contains no plastics or polymers. However, check that lids and seals are also BPA-free. |
| Can nickel in 304 cause allergies? | In extremely rare cases, people with severe nickel contact dermatitis may react to prolonged skin contact with stainless steel. Drinking from a cup does not cause allergic reactions — the nickel is bound in the alloy and does not contact skin. |
| Is stainless steel safe for hot drinks? | Yes. SUS304 is stable at temperatures far exceeding boiling water (safe to 800°C+). Hot coffee, tea, and other beverages do not affect the steel's composition or safety. |
Frequently Asked Questions
Q: What does SUS304 mean on a stainless steel cup?
SUS304 is the Japanese Industrial Standard designation for 304-grade stainless steel, containing 18% chromium and 8% nickel. It is the same alloy as AISI 304 (US) and EN 1.4301 (EU). It is the global standard for food-contact stainless steel.
Q: How can I tell if my cup is 304 or 201?
Visually, you cannot tell the difference. The most reliable methods are: (1) request the Mill Test Certificate from the manufacturer, (2) use a stainless steel testing solution (acid spot test), or (3) send a sample to a lab for XRF analysis. A magnet test can provide a rough indication but is not definitive.
Q: Is 18/10 stainless steel better than 18/8 for cups?
For cups and tumblers, 18/8 (SUS304) and 18/10 (SUS316) perform nearly identically. The extra nickel in 18/10 provides marginally better corrosion resistance to salt and acid, but this difference is meaningful only in marine or chemical environments — not for drinkware.
Najor SUS304 Drinkware: Certified, Tested, Factory-Direct
Najor Cookware uses SUS304 as the default material for all stainless steel drinkware, verified by mill test certificates and third-party laboratory testing.
Material: SUS304 (18/8) — every batch verified by MTC
Certifications: FDA, LFGB (SGS/TÜV tested), DGCCRF, CE
Testing: Metal migration testing per EU 10/2011 and FDA 21 CFR
Product range: Cups, tumblers, mugs, bowls, plates — all SUS304
Verification documents: MTC, LFGB report, FDA declaration available on request for all orders
MOQ: 100 pcs/SKU (catalog) / 500 pcs (custom)
Contact: sales@najorcookware.com