Chrome vs vegetable vs chrome-free vs metal-free leather: what is the environmental difference?
No tanning method is automatically the most sustainable. Chrome, vegetable, chrome-free and metal-free tanning use different tanning agents, and they differ in water and energy use, wastewater load and finished-leather performance. In this ISA Voice episode, Keith Hill, Vice President Sustainable Business Development at ISA Next-Gen Materials, compares the four methods and explains why chrome tanning with trivalent Chrome III has remained the leading method for more than 100 years.
Last updated: October 2026
The four tanning methods at a glance
| Method | Tanning agent |
|---|---|
| Chrome tanning | Trivalent chromium (Chrome III) |
| Vegetable tanning | Tannins from trees or other plants |
| Chrome-free tanning | Chromium replaced by alternative tanning methods, usually aldehydes |
| Metal-free tanning (wet white) | No metals; most conventional metal-free leathers use glutaraldehyde |
What the episode covers
Keith Hill compares the four methods on the points brands most often ask about: how much tanning agent each needs, water and energy use, the chemical oxygen demand (COD) load each places on wastewater treatment, biodegradability and finished-leather performance, including whether the leather can be made waterproof.
He explains that the chromium used to tan leather is Chrome III, which is distinct from hexavalent Chrome VI. Chrome VI is harmful and can form if Chrome III is oxidised, which is why chromium chemistry and wastewater treatment are tightly controlled.
On biodegradability, he notes that lab tests have not shown a big difference between leathers made with different tannages. His conclusion is that every method has pluses and minuses, and that the environmental performance of leather depends on the whole tanning process, not only the name of the tanning agent.
ISA Next-Gen Materials continues to work with chemical suppliers on research into alternative tanning materials.
Chapters
- 0:00 Introduction and the two questions
- 0:49 The four tanning methods
- 1:51 Vegetable tanning
- 2:51 Metal-free and chrome-free tanning
- 3:44 Chrome tanning: Chrome III and Chrome VI
- 4:53 Biodegradability
- 5:24 Why chrome tanning remains the leading method
- 6:05 Closing
Full transcript
Transcript of the ISA Voice episode as recorded, with minor corrections to spelling and punctuation. Where the recording differs from current approved wording, the approved wording is used.
0:00 · Introduction and the two questions
Hello again everyone. My name is Keith Hill and I am the Vice President of Sustainable Business Development for ISA TanTec Industrial. Welcome to our fourth podcast in our ISA Voice series, addressing common questions we receive concerning sustainability topics. Today's podcast will discuss two sustainability topics that are related to each other. First, what are the sustainability differences between chrome-tanned, veg-tanned, chrome-free, and metal-free leathers? And second, what are the differences in water and energy used, the effluent treatment impact, the differences in biodegradability and performance advantages of each type of tanning method. Chrome-tanned, veg-tanned, and chrome-free and metal-free leathers are four very different methods to tan cattle hides, and differ from each other based upon different tanning agents used and the tanning methodologies.
0:49 · The four tanning methods
We can easily tell by their names that the tanning agent for chrome-tanned leather, for example, is chromium, whereas the tanning agent for veg-tanned leathers are tannins that come from trees or from vegetables. Chrome-free tanning means that chrome is replaced by alternative tanning methods, usually aldehydes. Metal-free tanning means that while no metals are used, there are glutaraldehydes used in most conventional metal-free leathers and they are commonly referred to as wet white. Glutaraldehydes have been used for many years as disinfectants, fixatives and preservatives. In regards to the ecological performance of these different tanning methods and the material performance differences, they can be summarized as follows.
1:51 · Vegetable tanning
Starting first with veg tanning. Tannins from trees used for the veg tanning of leather can lead to deforestation in order to produce large quantities and can take longer regrowth times. Also, production of the tanning agents require very large amounts of biomass. Vegetable tanning needs much more tanning agent with high material cost used as compared to chrome tanning and logistically costs more to transport with higher CO2 emissions. Vegetable-tanned leathers have also a higher chemical oxygen demand loading commonly referred to as COD, impacting effluent treatment which partly remains in the effluent even after treatment. Veg tanning also has higher water consumption than chrome or metal-free tanning. Vegetable tanning does not normally produce consistent quality across all applications in color or durability and is very firm in temper. It cannot also be used to make waterproof leathers.
2:51 · Metal-free and chrome-free tanning
Looking next at metal-free tanning and chrome-free tanning. Metal-free and chrome-free tanning has higher toxicology to aquatic organisms and are listed generally speaking in water hazard class WGK2. Some of the synthetic tanning agents can create absorbable organic halogens in the wastewater and in the sludge and has been classified in some cases as partly carcinogenic. Metal-free leathers have higher chemical oxygen demand also again COD and the COD is less biodegradable and some of it does remain in the discharged effluent. Metal-free and chrome-free tanning is also more energy intensive to produce. And like veg-tanned leathers, waterproof leathers are not able to be made on metal-free or chrome-free tanned leathers.
3:44 · Chrome tanning: Chrome III and Chrome VI
Looking now at chrome tanning. Chrome tanning conventionally is made with Chrome III, which is a trivalent chrome, which is what is used to tan leather and is a pure inorganic metal and has no adverse effects and is inherently non-toxic. It is, in fact, a trace element in humans and in animals. However, if Chrome III is oxidized, it can create Chrome VI which is hexavalent which is harmful and is cancerous. Chrome III can be eliminated with the state-of-the-art treatments of wastewater and does not create any other chemical oxygen demand or COD load to the effluent treatment wastewater. Chrome tanning does use less water than veg or metal-free tanning. Chrome tanning also uses less energy than veg or metal-free tanning. Chrome tanning makes it possible to obtain a product that is qualitatively excellent from all points of view from that of a tactile sensation to the mechanical properties the durability and it is able to make waterproof leathers consistently.
4:53 · Biodegradability
Now, in regard to the biodegradability of the various tanning types it is dependent upon the degree of tanning and the astringency of the tannins. However, there have been several tests run in various labs globally that do not show a big difference in the biodegradability of leathers made from these different tannages. As reviewed in our ISA Voice podcast number three, the biodegradability of leather in general is much better than materials made from petrochemicals.
5:24 · Why chrome tanning remains the leading method
There are pluses and minuses for all leather types and tannages, but because chrome-tanned leather has proven the most versatile, the lowest cost and is easier to treat in the wastewater compared to vegetable tannings and aldehydes used in metal-free and chrome-free tannages. The chrome tan leather has kept its leading role as a preferred method of tanning for more than 100 years now. ISA, as a tannery group, continues to work with industry-leading chemical suppliers in support of research and development of alternative tanning materials that will lead the way into the future of even more sustainable methodologies for tanning cattle hides.
6:05 · Closing
This concludes our fourth ISA Voice podcast. Thank you very much for taking the time to listen and we hope you found it informative. Our fifth ISA Voice podcast will be focused on the impact of plastics and commonly available materials such as vegan leather, synthetic leather, and faux leather, as well as an introduction to our brand-new sustainable bio-based product line named HyphaLite™. We look forward to seeing you then. Thank you.