What LightSpray Replaced

Before we get to the robots, it's worth understanding what they're replacing. A traditional running shoe upper typically contains 20 to 30 separate pieces—sometimes more. Fabric panels, overlays, laces, tongue, heel counter, reinforcements. Each piece is cut from larger sheets of material (creating waste), then stitched or glued together in a multi-step assembly process that can take days or weeks depending on the factory's capacity.

The environmental toll is significant. On's fully automated LightSpray process produces an upper with 75% fewer carbon emissions compared to its conventionally made equivalent model. LightSpray eliminates the inefficiencies by spraying a single 1.5-kilometre filament of recyclable TPU onto a foot form in three minutes.

And that's just the upper. With traditional manufacturing, you still need to attach it to the midsole with adhesive, add branding, quality-check each component, and ship the finished product halfway around the world.

Spray, Fuse, Done

Instead of cutting and stitching multiple fabric panels together, a robotic arm sprays a continuous polymer filament directly onto a shoe last, the foot-shaped form that gives shoes their shape. The arm traces precise paths across the last, depositing roughly 1.5 kilometres of material in a single unbroken sequence, building up a seamless, one-piece upper from scratch.

The entire process takes three minutes. Add another three for inkjet branding, and you've got a completed upper in six minutes total.

On's factory in Busan, South Korea, is a space solely dedicated to manufacturing LightSpray models. Korea has the highest number of robotics per capita in the world, which is precisely why On chose it as the location. What once required a single prototype unit built specifically for Hellen Obiri's winning run at the 2024 Boston Marathon has now scaled to production capacity 30 times that original output, with 32 robots working simultaneously.

The result? Made from just eight pieces—one upper, two midsole components, and five small rubber elements—the LightSpray Cloudmonster 3 Hyper weighs only 205g in a men's size 8.5. That's 90 grams lighter than the standard Cloudmonster 3, and roughly 85 grams lighter than most max-cushion trainers on the market.

What It Feels Like

We could talk technology all day, but none of it matters if the shoe doesn't work. So what's it actually like to run in a shoe built by robots?

Jamie tried them on and ran in them for the first time without disappointment. That "caressing" fit he describes is deliberate. The LightSpray upper eliminates all seams, overlays, plastic heel counters, and tongue. The fit is truly seamless, with the foot as one with the platform and zero distractions. The upper is actually sprayed over the upper edges of the midsole so it's unified with the platform, with the foot also sitting down in a sort of foam bathtub, locking it seamlessly.

"I instantly fell in love with this shoe on the first run," Jamie says. "I also prefer the ride to the previous Cloudmonster Hyper 2, a shoe that I put many miles into."

The Platform: Where the Magic Actually Happens

Whilst the LightSpray upper gets all the headlines, the midsole is where On made the most significant performance upgrade from the Cloudmonster Hyper 2.

The Cloudmonster Hyper range uses two foams: the bouncy, responsive Helion HF (a PEBA-based supercritical foam), and the more structured Cloudtec foam. The Cloudmonster Hyper 2 placed the Helion HF at the front of the shoe and the Cloudtec foam at the rear. The result? Sufficient response on the forefoot, but a disconnected feel, like one half of the shoe responded entirely differently to the other half.

Jamie explains the fix: "The Cloudmonster Hyper 3 places a layer of Helion HF along the entire length of the midsole and positions the Cloudtec on the entire length of the outsole. This provides a much more responsive feel along the entire length of the shoe, whilst also providing stability at the base of the shoe."

The two densities of Helion HF foams, Cloudtec elements, and surprisingly copious outsole for such a light shoe all play key roles. The lower layer is considerably firmer than the upper, with the upper layer more springy and softer. The lower layer clearly provides some stability as well as a kind of plateless response with the Cloudtec elements having some give.

At 45mm in the heel, this is a maximalist stack by any measure. Yet the shoe never feels ponderous or disconnected from the road. Unlike the ASICS Superblast 3, the lower layer and outsole are far more seamless in feel at the road whilst still providing plenty of pop. No mushy or slappy sensations. The Cloudtec elements collapse just enough to allow the foot to roll forward.

Notably, On chose not to include a carbon plate. This was deliberate. Training exclusively in carbon-plated shoes can make your feet "lazy", the plate does the mechanical work, which means your muscles and tendons don't have to. For a training shoe designed to be used multiple times a week over high mileage, keeping the platform plate-free preserves leg freshness and encourages natural foot strengthening.

Where It Fits in Training

Jamie thinks the shoe could do it all. "Intervals, tempos, long runs, everyday runs, it really has it all. However, personally I shall be using it on my long runs, and the days where my legs feel a bit beat up. On these days I crave a more responsive shoe, and the Cloudmonster Hyper 3 will provide that responsiveness whilst also maintaining stability when I am running at a slower pace. I am thankful to have a shoe like this in my rotation."

For context, Jamie covers 145km per week with two interval sessions, a tempo run, a long run, and all the easy miles in between. He's running at a level where inefficiencies in footwear show up immediately. The fact that he's reaching for the LightSpray Cloudmonster 3 Hyper on long runs and recovery days—sessions that make up the bulk of any training programme—speaks to its versatility.

The On Connection

Jamie's relationship with On goes back further than you might expect. He first became aware of the brand about 11 years ago at the 2015 Scottish Running & Cycling show at the SEC, drawn to the shoes due to their unique design with their iconic holes in the sole.

It wasn't until 2018 that he started taking the brand seriously. "Chris Thompson, a hero of mine, was the first to really show the capabilities of On's footwear, winning the Great Scottish Run twice in a row whilst wearing the Cloudracer 2."

He first wore On shoes in 2024, and it's been a consistent part of his rotation ever since. "Not only do they make outstanding footwear, their commitment to supporting 'the little guy' means a lot to runners in my position. On have supported me in races over the last couple of years, and I thank them unreservedly for allowing me to taste the pro lifestyle."

His favourite race shoe? The Cloudboom Echo. "Carbon-plated shoes typically have large midsoles which make you feel like you're walking on the moon. Having run in a period before super shoes, these ultra-high midsoles felt very unnatural. The Cloudboom Echo is my favourite as it maintains that feeling of an old-fashioned racing shoe, whilst providing you with all the benefits of the modern-day carbon-plated race shoe."

But for training? "I have particularly enjoyed the Cloudmonster Hyper range on my Sunday long runs. This shoe is my training partner on a Sunday long run and helps me when the going gets tough."

The variation in On's product range is what keeps him coming back. For longer races, the Cloudboom Strike offers softer cushioning and promotes economy. For shorter races, the Cloudboom Echo gives that striking response from the ground when you need to up the pace. For everyday shoes, the Cloudsurfer range provides lovely soft cushioning when legs are beat up after a hard session. And for longer runs, the Cloudmonster Hyper is extremely responsive and becomes your best friend when you get deeper into the run. There really is a shoe for all needs.

The Fit: What You Need to Know

The LightSpray upper is laceless. There's no tongue, no traditional lacing system, no adjustment points. You pull it on like a sock, and the upper adapts to your foot through its engineered structure and thermal-bonded fit.

Jamie describes the process: "Putting on the shoes is quick, smooth, and simple." Though his first impression was that the shoe wouldn't provide sufficient restraint around the foot, and that his foot would move around when running, that wasn't the case. "The shoe felt glued to my foot. I especially enjoy cornering in this shoe as it feels incredibly comfortable and smooth throughout the movement."

For some, this is perfection. The feeling of no tongue, no laces, no overlays, no heel counter, with the entire upper a single material, is truly seamless and comfortable and reduces weight.

For others, particularly those with wider feet or high arches—it requires consideration. LightSpray's lace-free, form-fitting design is a technical achievement, but laceless shoes ask a lot from the sock system and upper structure to keep things locked down during dynamic movement, especially on descents.

On includes an Elite Run Sock High Hyper with each pair, designed to work in conjunction with the open upper structure. The LightSpray upper itself is porous by nature, so temperature regulation should be strong.

One practical note: getting them on can be challenging. Testers wished On could make this more user-friendly. Taking them off, however, is effortless with no laces in the mix.

Jamie weighs in on aesthetics: "Aesthetically the shoe is stunning. I would not advise considering the aesthetic of the shoe when purchasing running footwear; always choose the shoe that best suits your needs as a runner, however an aesthetically pleasing shoe is a bonus. I am a fan of wearing light-coloured shoes and socks as it makes me feel light on my feet and more relaxed when I am running."

The LightSpray Cloudmonster 3 Hyper launched in a Limelight/Bloom colourway—white upper with black branding on yellow CloudTec tooling. On co-founder Caspar Coppetti has described the shoe as what a shoe from Apple would look like, and looking at the design, it's hard to argue with the visual analogy.

What Running Gives Back

Winning last year's Glasgow Half Marathon is one thing. But showing up six days a week, 145km of training, balancing full-time work with elite-level competition, that requires something deeper. We asked Jamie what running gives him that other things don't.

"Running has given me so much in my life. As a youngster, it gave me self-confidence, and throughout my running journey, I have become a more driven, assured, and disciplined person. It has taught me the effectiveness of working hard to achieve a desired goal, and I have taken this into other areas of my life with a view to being successful.

"Running has been a constant in my life for as long as I can remember, and this has helped me through many difficult times. It has always been something I can fall back on when times are tough. The clarity you receive on a run has helped me solve many issues I have faced.

"Within the sport I have been successful, but what I value most from running is the friends that I have made, the amazing experiences I have enjoyed, and the healthy lifestyle that I live."

Jamie started running in 2010, begrudgingly joining his primary school cross-country club in Primary 6. A keen footballer, the thought of running didn't interest him at all. But the more he went to sessions, the more he enjoyed it, and the better he became. "I quickly became addicted to the thrill of running and the gratification of improving my ability. These fundamentals have kept me motivated over the last 16 years, and the enjoyment of bettering myself has never wavered."

That consistency has paid off. Multiple Scottish championships (junior and senior), international competition for Scotland, NCAA Division 1 running in the USA, one of the highest levels of competition in the sport. He's since returned to Scotland to continue competing at the highest level possible whilst working full time as a civil engineer.

His main goal over the next 12 months? Break 14 minutes in the 5K (current PB 14:04), run personal bests in the 10K (current PB 29:29) and 3K (current PB 8:13). But what drives him most is his competitive spirit. "I love racing. I love doing everything in my power to win a race. Therefore, my lifetime goal is to win the Scottish National Cross Country Championships. This is the crown jewel of running in Scotland, and a race I have dreamt of winning since my early days in the sport."

Beyond road and track, Jamie is looking forward to the famous Lairig Ghru trail race from Braemar to Aviemore this year. "My entire running career has been focussed on the road, track, and cross country, however, running on the trails is the most enjoyable! Especially in this amazing country where we are spoiled for off-road running opportunities. The Lairig Ghru will be my first attempt at a long-distance trail race, and whilst I see this as a bit of fun, I still plan to be competitive in this race!"

Finding the Right Shoe

Jamie's advice to newer runners looking for the right shoe is straightforward.

"Go to your local running store! Finding the right shoe can be the difference between enjoying your first running experience and giving up before you have even started. There are so many running shoes, and there are so many people online telling you what the best running shoes are. However, the best running shoes for one person will be different to the best running shoes for you, and it can be extremely confusing to know what running shoes are best for you.

"You could end up spending a lot of money on shoes that are not right for you, and you may even end up with a serious injury. Running stores, such as Achilles Heel, are full of extremely knowledgeable staff who can assist you in finding the best running shoe for you."

Should You Buy It?

The LightSpray Cloudmonster 3 Hyper builds on technology first seen in the Cloudboom Strike LS, the race shoe Hellen Obiri wore to win the 2024 Boston Marathon. This is its first application in a training shoe, a shift that brings robot-sprayed construction to the sessions that make up the bulk of serious running.

At £270, it's expensive. But you're paying for more than just a shoe. You're paying for a manufacturing process that took five years to develop, a dedicated factory in South Korea, an R&D team of 400 specialists, and a vision of localised, sustainable production that could reshape the entire footwear industry.

More importantly, you're getting a training shoe that actually works. Light enough to feel fast, cushioned enough for high mileage, stable enough for easy days, responsive enough for tempo efforts. A shoe that competitive runners like Jamie Burns, last year's Glasgow Half Marathon champion and a former member of the Achilles Heel team—are reaching for on their hardest training blocks.

The LightSpray Cloudmonster 3 Hyper is available now at Achilles Heel on Great Western Road. Come try it on, feel the seamless upper, and decide if the technology actually suits your training. We'll talk you through how it works, where it fits in a rotation, and whether it suitable for your running.