A 5.6-ounce marathon shoe leaves little room for conventional construction. The On LightSpray Cloudboom Strike 2 saves weight partly by having a robot form its seamless, laceless upper directly on the shoe in approximately three minutes.

The LightSpray process deposits a continuous 1.5-kilometer filament onto the midsole, producing a one-piece upper without seams or glue. Its close, second-skin fit removes the tongue and lacing system found on a conventional racing shoe. Each pair also includes On’s Elite Run Sock High Hyper.

Underfoot, the Cloudboom Strike 2 introduces a Helion HF superfoam material that On says is 15 percent lighter than its predecessor. A curved carbon Speedboard sits between two densities of foam and is both lighter and stiffer than the previous version. The new CloudTec Sphere geometry uses precisely engineered channels that expand and contract, allowing the midsole to flex and rebound while preserving a relatively uninterrupted profile.

The finished shoe weighs 158 grams, or approximately 5.6 ounces, with a 5mm heel-to-toe drop and a high-grip rubber outsole. Those figures place it well below the weight of the earlier carbon-plated marathon racer while retaining a platform developed for half-marathon and marathon competition.

The On LightSpray Cloudboom Strike 2 is priced at $310 in unisex sizing. On’s U.S. store currently shows limited inventory in select sizes, with availability notifications offered for the remainder.