Our verdict

The On Cloudflow 4.0 emerges as an impressive evolution from its predecessor, albeit catering to a niche audience with its firm midsole and form-fitting upper, sidelining a significant number of runners. Priced steeply at £170, we think it excels as a versatile neutral shoe for those it fits, delivering stability and a responsive, rockered run. Furthermore, the fact that it's one of the lightest daily trainers on the market enhances its attractiveness, in our view.

Pros

  • No longer catches stones in the outsole
  • Extremely light and nimble
  • Effective rockered geometry
  • Provides a stable ride
  • Comfortable and durable upper
  • High-quality materials
  • Suitable for interval training speeds

Cons

  • Likely too expensive for the features provided
  • Narrow midfoot fit
  • The foam may be excessively firm

Audience verdict

91
Superb!

Who should buy

The On Cloudflow 4.0 presents itself in the lab as an interesting choice for:

  • On fans seeking a versatile daily trainer suitable for various paces and distances.
  • Individuals looking for a lightweight running shoe versatile enough for occasional racing.
  • Runners with a narrow foot profile and a generous budget who value exceptional build quality.

On Cloudflow 4.0

Who should NOT buy

If you love roomy shoes or have wide feet, we believe the Cloudflow 4.0 may not be suitable for you. However, there are great alternatives in the premium daily trainers category, such as the Nike Invincible 3 or the On Cloudmonster.

On the other hand, perhaps you're drawn to the CF 4.0 for its low weight, yet desire a soft, cloud-like feel. Well, that's something this shoe doesn't provide based on our lab tests. In such instances, the ASICS Novablast 3 or the Saucony Endorphin Speed 3 may be more fitting choices.

On Cloudflow 4.0

Breathability

Upon unboxing the On Cloudflow 4.0 in the lab, we immediately observed that On had incorporated many features into the upper from their premier marathon racer, the On Cloudboom Echo 3, suggesting excellent breathability.

We assessed the breathability using our smoke-pumping machine in the lab and awarded it a 4/5.

While not the top score that the high-priced, blazing-fast Echo 3 garnered, it's still a great result and ensures optimal ventilation for summer runs.

Next, we conducted the light test. Here, we discovered that the shoe didn't have visible ventilation holes. However, we observed that the transparency extended into the midfoot area, ensuring optimal ventilation for the entire foot.

On Cloudflow 4.0 microscope

Curious about how this On maintained good airflow without any visible ventilation holes, we turned to our microscope.

On Cloudflow 4.0 close up

We determined that On uses a two-layer, thin engineered mesh that allows air to flow through. 

The crucial element for this upper is its minimal thickness. We believe that if it were slightly thicker, the ventilation would be severely compromised.

Test results
Cloudflow 4 4
Average 3.8
Compared to 221 running shoes
Number of shoes
1
Breathability
5

Durability

Toebox durability

The absence of large ventilation holes often leads to impressive durability, as there are no weak points in the robust upper.

This is precisely the case with the Cloudflow 4.0, which we validated in our rigorous Dremel test. Not many shoes achieve such a fantastic 3/5 score!

On Cloudflow 4.0 Toebox durability
Test results
Cloudflow 4 3
Average 2.3
Compared to 155 running shoes
Number of shoes
1
Toebox durability
5

Heel padding durability

Our enthusiasm soared after the initial test, but it quickly deflated during the subsequent Dremel evaluation.

In the heel test, the CF4 revealed its vulnerabilities, earning a disappointing score of just 2/5 from us.

On Cloudflow 4.0 Heel padding durability
Test results
Cloudflow 4 2
Average 3.2
Compared to 151 running shoes
Number of shoes
1
Heel padding durability
5

Outsole hardness

As we continued to evaluate the outsole's durability, we found that the rubber was harder than the average shoe. We measured its hardness at 85.4 HC using our Shore C durometer in the lab.

On Cloudflow 4.0 outsole

The outsole no longer features deep cutouts, ensuring that the CF 4.0 avoids trapping stones, unlike other On shoes.

This hardness aligned with what we expected from the Swiss brand. Given the shoe's design, it concentrates the runner's weight on a smaller surface area. The rubber simply needs to withstand more weight compared to most other shoes.

On Cloudflow 4.0 Outsole hardness
Test results
Cloudflow 4 85.4 HC
Average 80.4 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 272 running shoes
Number of shoes
54.9 HC
Outsole hardness
92.8 HC

Outsole durability

In our final test using the Dremel, the outsole took center stage. We discovered that, even though it's made of a harder rubber—which downgrades grip—the 1.0-mm indentation created is a disappointing outcome.

It's not extremely alarming, and the outsole is not going to fall apart after 200 miles, but we expect more from a daily training shoe.

On Cloudflow 4.0 Outsole durability
Test results
Cloudflow 4 1.0 mm
Average 0.9 mm
Compared to 133 running shoes
Number of shoes
0.0 mm
Outsole wear
2.0 mm

Outsole thickness

The team at On is obviously experienced and conducts a huge series of tests before placing any shoe on the shelves.

That's probably why they've included a thicker-than-average rubber to offset potential durability issues. This approach is effective, but it comes with a trade-off: a slightly heavier shoe.

On Cloudflow 4.0 Outsole thickness
Test results
Cloudflow 4 3.7 mm
Average 3.2 mm
Compared to 291 running shoes
Number of shoes
0.0 mm
Outsole thickness
6.6 mm

Weight

Weighing in at a mere 8.6 oz (245g), the Cloudflow 4.0 is a remarkably light shoe, even with its robust outsole.

This is an impressive 0.7 oz (20g) lighter than the Cloudflow 3.0.

On Cloudflow 4.0 Weight
Test results
Cloudflow 4 8.64 oz (245g)
Average 9.38 oz (266g)
Compared to 292 running shoes
Number of shoes
5.26 oz (149g)
Weight
12.56 oz (356g)

Cushioning

Heel stack

Due to the unique On Cloud system, we had to use a small hack to accurately measure the height at the official point specified by World Athletics. This is how we determined the 36.1 mm, indicating a substantial stack height beneath the heel.

Nonetheless, one shouldn't anticipate in this On the same amount of foam underfoot as seen in a standard midsole. The clouds invariably offer slightly less cushioning.

On Cloudflow 4.0 Heel stack
Test results
Cloudflow 4 36.1 mm
Average 33.6 mm
Compared to 291 running shoes
Number of shoes
7.6 mm
Heel stack
42.7 mm

Forefoot stack

Fortunately, the forefoot aligned perfectly with a complete "cloud," so we didn't need to make any adjustments and simply conducted a standard measurement. We determined the result to be 28.2 mm, which is more than sufficient for any forefoot or midfoot striker.

On Cloudflow 4.0 Forefoot stack
Test results
Cloudflow 4 28.2 mm
Average 24.9 mm
Compared to 291 running shoes
Number of shoes
7.6 mm
Forefoot stack
35.8 mm

Drop

On told us that the official drop was 8 mm, and after meticulously following the official WA guidelines, we measured an impressively close 7.9 mm.

Kudos to them for being one of the select brands with such precise and accurate drop statements.

On Cloudflow 4.0 Drop
Test results
Cloudflow 4 7.9 mm
Average 8.7 mm
Compared to 291 running shoes
Number of shoes
-0.8 mm
Drop
16.1 mm

Insole thickness

We clocked the insole thickness at 4.1 mm, a typical measurement for any daily trainer. Just an average approach by On.

On Cloudflow 4.0 Insole thickness
Test results
Cloudflow 4 4.1 mm
Average 4.5 mm
Compared to 287 running shoes
Number of shoes
1.5 mm
Insole thickness
7.3 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

While the midsole system is named "CloudTec," it surprisingly delivers a different experience from its name. Is crafted from two distinct Helion foams, and our durometer showed a softness of 28.3 HA for the main one.

However, this characteristic isn't necessarily negative. Contrary to the common belief that softer is better in running shoes, a firm midsole offers its own unique advantages such as enhanced stability, superior ground-feel, and foot muscle development.

On Cloudflow 4.0 Midsole softness
Test results
Cloudflow 4 28.3 HA
Average 21.4 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 219 running shoes
Number of shoes
8.5 HA
Midsole softness (soft to firm)
41.5 HA

Secondary foam softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

The supplementary Helion foam, positioned closer to the foot, ranks among the firmest midsoles we've assessed in our lab (33.0 HA).

Again, this isn't necessarily a drawback for all, especially when paired with On's CloudTec system. However, it's important to note that this combination is best suited for individuals who prefer a firmer feel over softer foams.

On Cloudflow 4.0 Secondary foam softness
Test results
Cloudflow 4 33.0 HA
Average 25.2 HA
We use an average of four tests. The photo shows one of those tests.

Difference in midsole softness in cold

We placed the shoe in the freezer for 20 minutes and then reevaluated its softness. This method allows us to observe the foam's behavior.

In the case of the primary Helion slab, it changed to 33.0 HA. Interestingly, this is the same measurement we recorded for the secondary foam at room temperature.

That's merely a 16.8% increase, an excellent outcome that aligns perfectly with our expectations for a premium shoe that retails at a premium price.

On Cloudflow 4.0 Midsole softness in cold
Test results
Cloudflow 4 16.8%
Average 25.6%
Compared to 218 running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Stability

Lateral stability test

As we mentioned earlier, a firm midsole can transform a shoe into a stable one, and that's exactly what happens with the Cloudflow 4.0.

The Cloudflow platform's built-in stability, aided by the Speedboard plate and the rockered geometry, ensures that we keep our form even in the longest runs, all while providing a subtle, pleasing responsiveness.

Torsional rigidity

The previously mentioned Speedboard plate is a crucial element contributing to the torsional rigidity of this shoe, which we have given a rating of 4/5.

Test results
Cloudflow 4 4
Average 3.2
Compared to 270 running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

The heel counter is quite flexible, earning a score of 2/5 from us. It appears that On aimed to craft a comfortable daily trainer, opting not to enhance stability by stiffening this area.

Individuals experiencing Achilles issues will surely appreciate this feature and the fact that the heel collar is greatly padded!

Test results
Cloudflow 4 2
Average 2.8
Compared to 254 running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

Next, we'll examine the dimensions of the midsole.

In the forefoot, we noticed On's distinctive narrow design, coming in at just 110.0 mm. 

On Cloudflow 4.0 Midsole width in the forefoot
Test results
Cloudflow 4 110.0 mm
Average 113.6 mm
Compared to 292 running shoes
Number of shoes
100.5 mm
Midsole width in the forefoot
126.5 mm

Midsole width in the heel

Shifting our attention to the heel, we observed that On has been slightly more generous, offering a width of 89.7 mm. This approach ensures secure landings, even for heel strikers.

On Cloudflow 4.0 Midsole width in the heel
Test results
Cloudflow 4 89.7 mm
Average 90.5 mm
Compared to 292 running shoes
Number of shoes
74.9 mm
Midsole width in the heel
106.6 mm

Flexibility

Stiffness

The Speedboard plate in the midsole makes the shoe quite rigid torsionally, as we explained before. However, it doesn't have the same effect longitudinally, which might be surprising to some.

In our lab's bend test, where we apply force until the shoe bends at a 90-degree angle, it only took 22.0N of force from us! This indicates that the plate doesn't make the shoe uncomfortable at all for walking or gym workouts.

Test results
Cloudflow 4 22.0N
Average 29.3N
We use an average of four tests. The video shows one of those tests.
Compared to 274 running shoes
Number of shoes
2.2N
Stiffness
94.4N

Difference in stiffness in cold

We repeated the test after placing the shoe in the freezer for another 20 minutes, and it certainly became stiffer, as we needed to apply 28.4N of force this time.

That's a 29.2% increase, which, as we've seen before, outperforms most shoes on the market.

Test results
Cloudflow 4 29.2%
Average 36.3%
Compared to 274 running shoes
Number of shoes
0%
Difference in stiffness in cold
148%

Size and fit

Toebox width at the widest part

The toebox, at its widest, measures just 95.7 mm, making this shoe ill-suited for individuals with wide feet.

On Cloudflow 4.0 upper

Those with medium-width feet should appreciate a snug fit, while it's an ideal choice for runners with narrow feet.

On Cloudflow 4.0 Toebox width at the widest part
Test results
Cloudflow 4 95.7 mm
Average 98.3 mm
Compared to 292 running shoes
Number of shoes
89.5 mm
Toebox width at the widest part
109.1 mm

Toebox width at the big toe

However, the toe area is unexpectedly spacious, measuring 79.4 mm.

This provides ample room for toe splay, even for individuals with Roman or Germanic feet—those whose toes don't have significant length differences.

On Cloudflow 4.0 Toebox width at the big toe
Test results
Cloudflow 4 79.4 mm
Average 78.0 mm
Compared to 166 running shoes
Number of shoes
60.4 mm
Toebox width at the big toe
92.5 mm

Tongue: gusset type

The tongue features a bootie-style construction, a preferred choice for many of On's running shoes. And it effectively prevents unwanted movement during high-speed runs or frequent cornering.

On Cloudflow 4.0 Tongue: gusset type
Test results
Cloudflow 4 Bootie

Comfort

Tongue padding

The shoe's design is focused on being lightweight, and one easy way to achieve this is by reducing the padding in the tongue (2.5 mm).

Unfortunately, this approach can cause issues such as lace bite during long workouts. We believe a slightly padded option would have been more interesting, even if it added a few extra ounces.

On Cloudflow 4.0 Tongue padding
Test results
Cloudflow 4 2.5 mm
Average 5.6 mm
Compared to 289 running shoes
Number of shoes
0.5 mm
Tongue padding
14.2 mm

Heel tab

The quest for weight savings presumably led to the omission of a cool heel tab.

On Cloudflow 4.0 Heel tab
Test results
Cloudflow 4 None

Removable insole

The insole can be easily removed, but it's important to note that not all third-party insoles or over-the-counter orthotics may fit seamlessly inside the Cloudflow 4.0.

The shoe's design, characterized by a narrow body paired with a wide toe cap, could potentially limit compatibility with certain insoles.

On Cloudflow 4.0 Removable insole
Test results
Cloudflow 4 Yes

Misc

Reflective elements

At a price of £170, we anticipated that On would include at least a couple of reflective strips on the shoe for safety during night runs. Unfortunately, we were disappointed to find... none.

On Cloudflow 4.0 Reflective elements
Test results
Cloudflow 4 No