The Fellow Stagg XF is the double-walled sibling of the Stagg X, designed for a specific complaint about the original: in cold kitchens, the single wall loses heat fast enough to affect the last minute of extraction. The XF answers that with a vacuum-insulated stainless body that holds slurry temperature noticeably better than any other dripper in its class.
Beyond the wall, the XF keeps everything that made the X work: tapered flat bed, engraved ratio guide, #4 wedge-compatible filters. Recipes move straight across from the X with one practical difference — because the thermal mass is higher, skipping the pre-heat rinse has a smaller impact than on the X. You can still do it and probably should, but the XF forgives the oversight.
Use 22 g of coffee, 350 g of water (1:16), medium grind, water at 93–95 °C, three to four pours in 3:00 to 4:00. The cup is marginally sweeter and fuller than the X at identical inputs, which some brewers treat as a feature and others as a reason to coarsen the grind half a notch. It is the Stagg to choose if your kitchen runs cold or you brew for someone who likes a slightly more rounded cup.