The fabric is constructed with a reactive dyed warp so that the colour will not fade over time with wear. As is always the case with Iron Heart, the details are spot on. Triple chain stitch construction and vintage-style cat's eye buttons make for a classic work shirt.
In a reactive dye a chromophore contains a substituent that is activated and allowed to directly react to the surface of the substrate. Reactive dyes have good fastness properties owing to the bonding that occurs during dyeing.
Reactive dyes are most commonly used in the dyeing of cellulose like cotton or flax, but also wool is dyeable with reactive dyes.