Iron Heart’s UHR (an acronym for “Ultra Heavy Raw”) selvedge denim enjoys legendary status among aficionados and fans of the brand — renowned for its rich fading potential and dense weave.

The creation of UHR was a rather happy accident. Haraki-san had already set the benchmark with his original 21oz double-twisted weft yarn denim and was experimenting with designs for another fabric similar to his signature weave. However, he (rather fortuitously, in hindsight) made an error in his calculations, and the resulting denim is what we now know as UHR.

A very different beast from our flagship 21oz denim, UHR is an unsanforized “loomstate” denim — somewhat of a rarity in the Iron Heart range. This means that its woven weight is calculated at 23oz per square yard, but once soaked or washed, the yarns contract, tightening the weave to become a denser 21oz. Haraki-san originally christened his new creation “21/23” denim, released only in the 634-cut jeans in Japan. As more cuts were added, it earned the name Ultra Heavy Raw to differentiate it from other denim of a similar weight.

UHR denim is actually produced in only one mill in Japan — a husband-and-wife team with a “house” factory containing just four looms, only two of which can weave UHR. On top of that, as it is located in a residential area, the looms are only allowed to run for eight hours a day, producing just 0.8 rolls (50m) daily. When you consider it takes 2.8 metres of denim to make a single pair of jeans, you begin to understand why UHR denim is so limited — and so sought after.

For anyone new to the selvedge scene, this is not a denim for the faint-hearted. Being a raw weave, UHR jeans are designed to shrink when initially washed or soaked, making sizing a little trickier compared to sanforized denim. But the end result is worth the effort. Once broken in, UHR denim softens and moulds to the wearer’s body like no other — warmer than our flagship 21oz, softer than 25oz XHS denim, and as comfortable as your favourite pair of sweatpants. While there are often lengthy gaps between restocks, we now produce all our core jean cuts in UHR denim — explore the full range now.