On Cloudboom Strike LS Review: The Laceless Race Shoe Built by a Robot

Introduction

On has spent around five years developing a manufacturing process it calls LightSpray, and the Cloudboom Strike LS is the first racing shoe to come out of it. Instead of cutting, stitching and gluing separate panels, a robot sprays a continuous polymer filament to build the entire upper in roughly three minutes, then bonds that upper directly onto the midsole. The result is a laceless shoe with a second-skin fit and an upper that weighs just 30 grams, less than half of On’s previous lightest. Limited numbers have already reached runners, and elite athletes are expected to race in it at a major event this summer.

What makes the shoe worth a closer look is not one feature but the combination: a sprayed upper, no laces, and a bond between upper and midsole that removes several traditional construction steps. That is a different way of assembling a running shoe rather than a small refinement of an existing racer.

Who This Shoe Is For

The Cloudboom Strike LS is aimed squarely at runners chasing speed on race day. The platform is built from the bottom unit of the Cloudboom Echo 3, On’s first true super shoe, which already carried the high-performance elements the LightSpray project set out to evolve.

Triathletes get particular attention here. Because the shoe has no laces, it is quick to step into, and On added a top cloth similar to the surface of a sockliner that sits directly on the foam. That detail exists for athletes coming straight off the bike and slipping into the shoe barefoot, and it also reduces slipping inside the shoe.

If you race regularly, care about weight above almost everything else, and already know your size in On racing shoes, this is the shoe the design is pointed at. If you are looking for a daily trainer or a shoe you can adjust on the fly, it is not.

Main Strengths

Three things define the Cloudboom Strike LS: the sprayed upper, the very low weight, and a race platform carried over from a proven super shoe.

LightSpray: The Robot-Spun, Laceless Upper

The upper is created from a single continuous filament sprayed into shape. On describes the process as being able to refine the fit, the elasticity and the positioning of the material, all in service of performance. The shoe has no laces at all, which is why the upper can be so light.

Because the upper is welded seamlessly to the midsole, there is no need for a sockliner. Running directly on the foam is unusual, and it is also what allows On to push the super foam stack height to the maximum in this shoe.

The development process leaned heavily on athletes. Early prototypes went to internal runners first, then to external athletes, so the theory could be checked in practice. Because LightSpray produces a prototype in minutes rather than weeks, On could build a version, test it, collect feedback and data, and have a new version on an athlete’s feet the next day. That speed is a real part of how the final shoe was shaped.

Weight, Stack Height and Race Geometry

The numbers matter here. The Cloudboom Strike LS weighs 170 grams in a US men’s 8.5 and 158 grams in a US women’s 7. The stack sits at 39 mm at the heel with a 4 mm drop to the forefoot.

Underneath, the bottom unit follows the Cloudboom Echo 3 closely. It uses the same core elements: On’s performance foam, a carbon Speedboard and an outsole. The upper is then created and welded directly onto that bottom unit, so the two halves of the shoe are joined in one continuous step rather than assembled afterwards.

Things to Consider Before Buying

The laceless design is the headline feature, and it is also the thing to think through carefully. Fit is created by the sprayed upper rather than adjusted by laces, so there is no way to loosen or tighten the shoe on the run. Getting your size right matters more than usual.

Running without a sockliner is another adjustment. The top cloth sits directly on the foam, which is designed to feel closer to the ground and reduce slipping, but it is a different underfoot experience from a conventional racing shoe with an insole.

Availability is the other practical point. Production has been limited, and the shoe has been prioritised for elite athletes ahead of a major summer event, so pairs have been hard to find.

Finally, it is worth treating this as a specialised race tool. Everything about the design serves low weight and fast running, and that focus is deliberate rather than a compromise to work around.

Buying Advice

If you race and want the lightest setup you can get, the Cloudboom Strike LS is a genuinely different proposition. The upper is the lightest On has produced, the weight is competitive for a super shoe, and the midsole and carbon plate come from a platform that has already proven itself.

The sensible approach is to buy it as a race-day shoe, not an everyday one, and to be confident about your size before committing, since the fit is fixed by the upper. Runners who like to fine-tune lace tension may find the laceless construction takes some getting used to.

Availability and Release Timing

Limited numbers of the Cloudboom Strike LS have already been released, and another limited run is planned for the fall. Beyond that, On intends to move to broader distribution in the future, which should make the shoe considerably easier to find.

If you want a pair for a specific race, the practical advice is to watch for each release window rather than assume stock will be sitting on shelves. When the wider distribution arrives, the shoe will be a more straightforward purchase for anyone who has been curious about the laceless design.

Conclusion

The Cloudboom Strike LS is one of the more unusual racing shoes to appear in recent years. A robot sprays the upper from a continuous filament in about three minutes, the upper weighs 30 grams, and there are no laces to tie. Underneath sits a familiar and capable race platform with a 39 mm heel stack, a 4 mm drop, a carbon Speedboard and a race weight of 170 grams in a US men’s 8.5.

For competitive runners and triathletes who value low weight and a locked-in second-skin fit, it is a compelling race-day option. For everyone else, the limited availability and the fixed laceless fit are worth weighing up before you commit.