Østmo boots are made using a combination of double row stitchdown and naildown construction. The back half of the upper and midsole is nailed down to the insole using brass clinching tacks, which create little hooks that hold everything together securely. Brass does not oxidize or rust like the more commonly used steel nails and tacks, and will not rot out the leather over time.

The forward part of the upper is flared out and stitched to the midsole with the lining and toe puff sandwiched in place between the insole and midsole. A second row of stitches then go through the flared out upper, midsole and outsole. Both the midsole and outsole stitches are done entirely by hand, which allows for better control over the stitch tension, making sure everything is put together in the most solid and consistent manner possible.

An added advantage of the flared out upper is how it wicks water and moisture away from the rest of the upper; and nothing is allowed to make its way into the interior of the boot. There is no such thing as a waterproof leather boot, but stitchdown construction is about as water resistant as it gets.

From start to finish, it takes about 50 work hours to make one pair of Østmo boots.

While the upper leather used for each pair of Østmo boots is always subject to change and will have their unique properties and qualities both aesthetically and functionally, the interior components ultimately play the biggest role as far as durability and long-term comfort is concerned. Each boot is built around a 4,5-5mm. vegetable tanned leather insole from the Spanish Splenda tannery. While firm from the get-go, it conforms to the foot over time and molds to the wearer's particular gait, resulting in a boot that should feel like home. The same can be said about the leather heel stiffener, which from late 2023 on is made from hand-cut full grain 3mm. veg tan leather from the renowned Swedish Tärnsjö tannery. And on the topic of Sweden, the lining used for Østmo boots is a supple but hefty aniline cowhide from the Elmo tannery, adding to both structure and comfort.

Like the insole, also the shank and the midsole consists of 4,5-5mm. Splenda sole bends. For bottom filler, from 2024 on, veg tan leather is used to fill the cavity between the lining and insole after the boots are lasted. 

The only non-leather component, apart from the hardware, of any given Østmo boot is the toe puff - if applicable. This is made from adhesive backed, thermo-activated, non-woven fabric that holds its shape better than its leather counterparts. Østmos are offered with unstructured toes (no toe puff), partially structured toes (0,5mm. toe puff) and structured toes (0,7mm. toe puff).

Most Østmo boots are finished up with a rubber outsole. The one most commonly used is Vibram Eton, a low profile studded sole. Other favorites include the Dr. Sole 1220 full sole and 1230 half heel, as well as the Vibram 430 mini-lug full sole.