What Is the CI Rating in Cold-Resistant Safety Shoes?

Cold environments don’t just hurt workers — they destroy shoes. Most buyers don’t find out until soles crack, grips fail, and contracts are lost.

CI stands for Cold Insulation. In EN ISO 20345¹, it marks safety footwear tested at -17°C² for thermal resistance, with a minimum insulation value of 0.25 m²·K/W. It means the shoe’s materials — especially the outsole — still perform under cold conditions, not just that the shoe feels warm.

Most buyers skip CI in their initial inquiry. They list toe cap type, slip resistance class, maybe ESD requirements. Cold insulation gets left off the spec sheet — until something goes wrong in the field. I’ve seen sole delamination at -25°C, outsoles that cracked under flex after one winter, and workers slipping on frozen ground because the rubber had gone stiff. Every one of those failures had one thing in common: no CI rating. This article breaks down what CI actually means, how it’s tested, how it compares across different certification systems, and why it matters more than most buyers think.

What Does CI Stand For in Safety Footwear Standards?

"Cold-resistant" sounds simple. But in footwear certification, it means something very specific — and most buyers don’t know the difference until a product fails.

CI stands for Cold Insulation. It is a defined marking under EN ISO 20345, the European safety footwear standard. A shoe carrying the CI marking has been tested to maintain a minimum thermal resistance of 0.25 m²·K/W³ when conditioned at -17°C. It is a performance rating, not a marketing claim.

Two years ago, a buyer from a cold storage company in the Netherlands contacted me. He had been sourcing winter safety shoes from another supplier for three years. The shoes had thick fleece lining, felt warm, and workers liked them at first. After one winter, the complaints started — soles cracking, workers slipping on frozen ground because the outsole had hardened and lost grip. He had no idea what CI rating was. When I explained that CI testing is about whether the shoe’s materials keep their performance at -17°C — not just whether the shoe feels warm — he immediately understood the problem. His previous shoes had no CI certification at all. We re-sourced his full order with CI-rated outsoles. The complaints stopped the following winter.

CI vs. "Winter Use" — What’s the Real Difference?

Many products on the market are labeled "winter use," "cold protection," or "suitable for low temperatures." These are marketing descriptions. They carry no certification requirement and no testable standard behind them. CI is different. It is a pass/fail rating tied to lab-tested performance data.

A distributor based in Finland told me last year that less than 30% of the safety shoes in his local market carry a verified CI marking. Most products claim cold protection in marketing materials, but when he checked the actual EN certification documents, CI was missing. He made CI a mandatory spec for all his cold-weather SKUs. Within one season, he had won three new corporate contracts — including one with a logistics company operating freezer warehouses at -22°C. CI is verifiable, auditable, and something serious procurement teams increasingly ask for by name.

How Is the CI Rating Tested and Measured?

A lot of buyers assume cold-resistance testing just means leaving the shoe in a freezer for a while. The actual test is more specific than that — and the part of the shoe being evaluated might surprise you.

CI testing under EN ISO 20345 conditions the complete shoe at -17°C, then measures thermal resistance through the insole. The outsole is also subjected to flex testing at -17°C. The shoe must achieve a minimum thermal resistance of 0.25 m²·K/W and the outsole must not crack under repeated flexion at that temperature.

Most people, when they hear "cold-resistant shoe," immediately think about the lining — Thinsulate, wool, fleece. That thinking is understandable. But in actual CI certification, what determines pass or fail is usually the outsole. I’ve had clients come to me after failing EN certification audits with their previous supplier. In three out of four cases, the outsole compound was the problem.

Why the Outsole Is the Critical Variable

Standard TPU outsoles begin to stiffen noticeably below -15°C⁴. Some cheaper rubber compounds become brittle at -20°C and crack under flex⁵. We use a cold-grade rubber compound blended specifically to remain flexible at -30°C. The difference in material cost between a standard rubber outsole and a cold-grade compound is roughly 8–12% of total shoe cost. That’s not a large difference. But it’s the variable that determines whether the shoe passes CI testing.

The thermal resistance measurement is taken through the insole using a standardized plate method⁶. The test simulates heat loss from the foot through the shoe to a cold surface. The shoe must maintain the minimum 0.25 m²·K/W value across the entire insole area, not just the heel or forefoot. This means both the midsole material and insole construction contribute to the result. A shoe with a CI-compliant outsole but a thin, low-density insole can still fail this part of the test. Both components have to be designed together with cold performance in mind.

Is ANSI Z41 Still Valid?

Buyers sourcing for the North American market still reference ANSI Z41 in specs and RFQs. If you’re doing that, here’s what you need to know.

ANSI Z41 was withdrawn in 2005⁷. It has been replaced by ASTM F2413, which is the current active standard for safety footwear in the United States and Canada. Any product certified only to ANSI Z41 does not meet current North American safety footwear requirements.

I still receive RFQs that list ANSI Z41 as the required certification — usually from buyers who have copied an old procurement template without updating it. When I see that, I flag it immediately. Supplying to an outdated standard is not a compliance solution. It creates liability for the distributor and risk for the end user.

ASTM F2413 vs. EN ISO 20345 — Cold Resistance Coverage

This is where North American buyers often run into confusion. ASTM F2413 covers impact resistance, compression resistance, metatarsal protection, electrical hazard, and puncture resistance. It does not include a standalone cold insulation rating equivalent to CI. There is no ASTM cold performance marking that directly matches what EN ISO 20345’s CI designation measures.

I had one client supplying a multinational oil company with sites in both Norway and Texas. The Norway site required EN ISO 20345 with CI marking. The Texas site required only ASTM F2413. We produced two separate SKUs — one dual-tested to EN with CI, one ASTM-only without. It added cost and lead time. If that buyer had understood this gap at the start of the sourcing process, the planning would have been cleaner. I now raise this in the first conversation with any client who has multi-region supply needs, before the spec sheet is finalized.

What Does the S7L Rating on Safety Boots Mean?

S7L is one of the newer markings appearing on EN-certified safety footwear. Buyers seeing it for the first time often ask what it adds over S3 or S5.

S7L is a safety footwear classification under EN ISO 20345:2022⁹. It indicates a full ankle boot with all S3 protections — steel or composite toe, puncture-resistant midsole, heel energy absorption, water resistance — plus additional requirements for lace retention and ankle support structure.

The 2022 revision of EN ISO 20345 introduced several updates to the classification system. S7 and S7L were added to recognize that ankle support and boot height have measurable impact on workplace injury outcomes¹⁰, particularly in construction, logistics, and outdoor industrial environments. Buyers who were previously specifying S3 HRO WR CI for cold, wet, outdoor environments should now consider whether S7L covers those needs more cleanly in a single classification.

Breaking Down the S7L Classification

S7L builds on the full S3 base protection and adds tested requirements for the boot structure itself, not just the protective components inside it.

For buyers supplying cold-climate markets — northern Canada, Scandinavia, the Baltics, Siberia — S7L with CI and WR is now the most complete single-boot specification available under EN ISO 20345:2022. In my experience, about 7 out of 10 new clients who come to me for cold-environment shoes don’t mention CI in their initial inquiry. They list toe cap standard and slip resistance, but cold insulation gets skipped. I had one client, a PPE distributor supplying construction sites in northern Canada, who had been selling non-CI shoes for two seasons. In his third winter, one of his end clients reported early sole delamination — the adhesive bond between midsole and outsole was failing at -25°C¹². He lost that contract. When he came to me, the first thing I asked was whether his previous shoes carried CI. They didn’t. We rebuilt his product spec from scratch, added CI and HRO rating, and he won back the client the following year. CI should be on the first line of the spec sheet for any cold-environment application — not something you discover after a product failure.

Conclusion

CI rating is not a comfort feature. It is a performance standard that determines whether a safety shoe keeps working when the temperature drops below -17°C. Understand it before your product fails in the field. At Shoegan, we build cold-rated safety footwear that meets EN ISO 20345 CI requirements — built to protect, made to last.