Sixteen iron blocks at 2.1 pounds each slide into front and back pockets, taking the vest from a 1.43 pound empty shell up to 35 pounds in increments small enough to progress week by week rather than jumping between fixed sizes. Loading is symmetrical across the chest and spine, so the mass stays centred during running, hiking, push-ups and loaded carries instead of swinging to one side. The shell is 1000D nylon, a dense weave that breathes, resists sweat and stays soft enough against skin to be worn over a training shirt without chafing. Padded shoulders spread the load off the trapezius, and adjustable side straps pull the vest tight to a wide range of torso sizes so it does not bounce. A quick-release metal buckle at the chest lets the vest come off in one motion at the end of a set. Reflective stripes raise visibility on early morning and evening routes.