New Balance Fresh Foam X Hierro v9 review

After testing the Hierro v9 on the trails and in the lab, we believe that it's:

• A dream come true for fans of the Hierro series who craved more underfoot cushioning—this version finally delivers it.  
• Ideal for trail runners looking for a plush-and-durable maximalist shoe built for long-distance outings.  
• Fantastic for midfoot and forefoot strikers, with upgraded forefoot foam and a low-drop setup that feels naturally efficient.

We believe that the Hierro v9 isn't the right pick for runners who loved the flexible, easygoing feel of past versions. It’s now a stiff-and-rigid trail shoe that trades natural motion for a max-cushion ride. In our view, shoes like the Nike Pegasus Trail 5 or Hoka Challenger 7 feel way more natural underfoot.

From our perspective, the 4.2 mm drop could be an issue for some heel strikers, as it means a big departure from the previous setup. We think they’d feel more at home in the Brooks Caldera 7 or even the ultra-high-drop Merrell Moab Flight.

With 37.3 mm in the heel, the New Balance Fresh Foam X Hierro v9 is no longer in the average category—at least not for now. We discovered it's 5.1 mm higher than the Hierro v8, putting it close to the 40 mm barrier—a height only a few trail shoes are starting to approach.

This is a great advantage for heavier runners or extreme heel strikers, especially for long-haul trail efforts. However, it also creates a less-grounded, stiffer feel that won't please everyone.

But it’s the forefoot that changed the most. Like… by a mile. In the Hierro v7, we measured 22.5 mm in this area, which increased to 24.1 mm in the Hierro v8—right around average.

Now, we’re jumping all the way up to 33.1 mm. That’s a massive 37% increase—a huge leap that we rarely see in our lab, even after testing hundreds of shoes each year.

We got further confirmation that New Balance is really reshaping the Hierro series with our drop measurement. It used to be a high-drop trail shoe, but now it’s basically the opposite.

At just 4.2 mm, the drop now caters to midfoot and forefoot strikers more than anyone else. From our perspective, heel strikers may find it less appealing, as the Hierro v9 feels like an Altra or Topo!

Carrying Fresh Foam X in the name, it seemed obvious to us that the midsole would lean toward cloud-soft territory. But with trail shoes, there's always a chance the foam will be tuned slightly firmer for stability.

That’s why we were fine with the 14.6 HA reading we recorded in the Hierro v9. In our tests, it felt quite protective without being overly squishy—a great combo for long-distance comfort and ultra events. However, as we expected from EVA-based designs, rebound is not very high.

Faced with 20 minutes of deep-freeze testing, the Hierro v9 held up surprisingly well—its midsole only got 24% firmer. It’s not a chart-topping result, but quite decent for an EVA-based material like Fresh Foam X.

The insole is the familiar standard version New Balance uses in many road-focused daily trainers, measuring 4.5 mm in thickness.

We found in the lab that brands often turn to rockered midsoles to offset the stiffness added by extra foam, especially once the forefoot surpasses 30 mm—so the Hierro v9 was a clear candidate for this curved shift.

True to our expectations, the Hierro is no longer flat. Both the heel and forefoot now feature a noticeable rocker, creating a more assisted, momentum-friendly ride—though it feels a bit less natural and more guided.

We already saw that the Hierro v9 brings much more foam underfoot. But is there also extra space in the toebox? Let’s find out using our ultra-precise gel-based measurement technique!

Starting with the widest part of the toebox, we don’t have great news for broader-footed runners. At 94.7 mm, this result aligns with an average fit, even leaning slightly on the snug side.

We noticed the same trend in the big toe area, which has a noticeably pointy shape even before taking measurements. After testing with our digital callipers, we found 73.4 mm. That's another below-average result for this zone.

However, there’s a catch. In some regions, New Balance offers the shoe in multiple widths, so if you’ve got wide feet, go for the 2E or even the ultra-roomy 4E version if available.

We also wanted to measure the vertical space for the toes—something our gel-based method handles with ultra-clear accuracy.

We discovered 26.7 mm, a middle-of-the-road result that should suit most runners. From our perspective, it’s a cautious design move by New Balance.

Some of you may be wondering if the Hierro’s much taller stack height has hurt its stability—but it hasn’t. The shoe has been completely reworked to stay decently stable, though it comes with some trade-offs we’ll break down next.

One of the biggest changes comes with the ultra-rigid torsional structure of this shoe. The Hierro v8 and earlier versions were really flexible, but that changed in version 9—it now scored 5/5 in this lab test.

That’s a result we usually see in carbon-plated racers, so imagine how rigid it feels on foot. We think that’s a deliberate move by New Balance to add support to the now towering platform, but it definitely trades off the relaxed flexibility of previous versions.

The heel counter stays moderately flexible—more like New Balance’s road models—and scored 3/5 in our test. It should work well for most runners, even those with sensitive heels or Haglund’s deformity.

The Hierro’s platform definitely got wider. This is one of the key changes that helped maintain a stable ride despite the sky-high stack. In the forefoot, we measured 116.9 mm versus 113.2 mm in the previous version.

The heel got wider too—94.1 mm compared to 91.9 mm. It’s not a dramatic change and barely noticeable underfoot, but it signals the Hierro’s shift toward a maximalist future.

Alongside its ultra-rigid torsional build, the longitudinal stiffness marks another dramatic shift in feel for the Hierro v9. Put simply—if you loved the flexible-and-natural vibe of previous versions, you’re in for a disappointment.

We tested it in our 90-degree bend test and recorded 34.6N—a massive jump from the 14.9N we measured in the v8. That’s a whopping 132% increase!

Another downside of this update comes with weight, growing from 10.5 oz or 298g to 10.9 oz or 309g. It may sound fair given the added foam and broader platform—but still, it’s extra baggage on an already heavy shoe.

We observed that New Balance made a commendable effort to enhance the toebox ventilation in the Hierro v9. This endeavour resulted in a moderate 3/5 score in our breathability assessment, which we consider well-suited for year-round trail adventures.

Upon placing the upper over our LED light, we noticed numerous openings in the toebox that facilitate airflow. However, the remainder of the shoe features a thicker construction aimed at providing additional stability to counter the added stack height.

We also employed our digital microscope to examine the mesh design. 

We identified substantial ventilation holes that effectively promote airflow; however, they may raise concerns regarding durability, which we will evaluate shortly.

The upper represents a significant improvement, offering generous padding in the heel and tongue areas.

It exhibits slight stretchiness and incorporates "Toe Protect" TPU reinforcements designed to prevent premature wear in the toe cap region.

We had some concerns about this test, since the mesh has so many ventilation holes—and those are often prone to tearing. However, New Balance nailed the material choice, and it scored a superbly 4/5.

It wasn’t easy to top the toebox score, but the Hierro v9 pulled it off by earning a flawless 5/5 in the heel padding test. That’s a strong signal this area won’t wear down easily!

Now, what about the outsole? New Balance has consistently relied on Vibram for the Hierro, though they’ve alternated between compounds—sometimes even using the underwhelming Ecostep, especially when compared against the fantastic Megagrip.

Fortunately, the Hierro v9 brings back Vibram Megagrip, which we think is a major win.

In our view, Megagrip is the gold standard in trail running, and with a firm 88.6 HC reading, it promises long-lasting durability paired with awesome traction across rugged terrain.

Our third Dremel test delivered a satisfactory result, showing 0.9 mm of damage. Not jaw-dropping by any means, but good enough that we won’t be flagging premature outsole wear as a red flag.

The outsole is also thick enough to shield the feet from sharp or uneven terrain, measuring 2.4 mm. This helps explain why the Hierro feels slightly firmer than expected for its durometer result—over 5 mm of rubber separates the midsole from the ground!

We found moderate lugs in the Hierro v9. At 3.3 mm, they clearly lean toward smooth, everyday trails rather than wild, highly-technical terrain.

In our experience, the combination of Vibram’s high-traction Megagrip compound and the tooth-edged Traction Lugs delivers a fantastic amount of bite on gravel, dirt, and even light mud. It’s a top outsole for moderate conditions.

However, this isn’t a go-anywhere tank. The tread design excels in multi-purpose settings but lacks the aggressive depth and spacing needed for slippery slopes or deep, loose ground.

There’s a small price jump from the Hierro v8, and that’s never exciting. However, it feels justified—this version packs way more foam and an upgraded, super-grippy Vibram Megagrip outsole. Sounds fair to us.

Unfortunately, the Hierro v9 comes without any reflective elements—just like v8. Looks like New Balance isn’t too excited about giving this trail shoe some night-friendly, hi-vis flair.

The Hierro v9 features a rugged, trail-ready lacing system with broad, flat laces threading through thick, textured loops and reinforced punched eyelets. A central tongue loop adds structure, helping the tongue stay centred during dynamic movement.

The tongue itself feels nicely padded, clocking in at 7.2 mm—plenty for long, bumpy miles. However, we weren’t too thrilled with the lowercase “hierro” branding. It looks like an afterthought!

The tongue is semi-gusseted. That's a good choice for trail running, as it blocks debris from sneaking into the toebox and boosts lockdown by stopping any unwanted tongue shifting.

Another change from previous Hierro models is the redesigned heel tab, now stitched asymmetrically to the side for added strength. Still, it does look a little odd, doesn’t it?

Despite having a meaningful message we agree with, the insole is pretty basic—so we were glad to find it’s easily removable and can be swapped for something more cushioned or supportive.