This is the hand welted construction.
One of the strongest construction and one of the hardest to execute.
I find this construction special and use it in most of my bespoke boots, as it can only be done by hand. A good year welt machine needs to stitch into a glued-on canvas rib to get the height for the machine to bite.
I have spent years honing my skills and finding the best leathers for the insole and welt and above all, finding the perfect thread to give my product durability and comfort.