Fox technically debuted the Union BOA Flat shoes back in the spring of 2024, and I reviewed them for another outlet at that time. But, for me at least, that first iteration was a bit of a miss. It had some fit and function issues that we’ll dive into later that meant it performed notably worse than other options on the market.

But earlier this year, without much fanfare, Fox released an updated version of the Union BOA Flat, with a few subtle changes that have had a big impact on its performance. I’ve been riding the new Union all summer, so it’s time to weigh in. But, honestly, that last sentence says it all: I only rode in the previous version for a few weeks before my frustration with its shortcomings made me hand it off to a buddy. The new version is miles better, and if you wrote off this shoe in the past, it deserves a second look now.

Fox Union BOA Flat Details

• Sizes available: 5-13
• Sole rubber: Ultratac™
• Size Tested: 9.5 US, 42.5 EU
• Price: $259.95

Fox Union BOA Flat Fit

As always, remember that foot shape and shoe fit is a very personal issue. But here’s my experience: I have wide, tall feet. Length wise, I can hypothetically fit in a size 9 from most brands, but the width and overall volume is rarely adequate. So I typically size up to a 9.5 or 10. I went with a 9.5, or 42.5 in the Union BOA Flat, and it’s right on the money for me. I’d say it fits slightly larger than a typical 9.5, and closer to a 10 from Specialized or Five Ten.

Fox includes customizable insoles with swappable arch spacers and D30 inserts for impact absorption. This is a nice touch, and should be the norm on premium shoes. Other brands, take notes.

Fox Union BOA Flat Features

First, we’ll take a quick lap through the Union’s feature set, and then talk about how it differs from the first generation, and why it’s better. The Union BOA is adjusted with two BOA Li2 dials and uses the textile BOA laces, instead of the steel cables found on the first generation. The Li2 dials are great, they allow for microadjustments in both directions, and using two per shoe makes it easier to dial in different fit zones. 

There’s a molded toe cap, and the shoe’s outer uses a combination of TPU and ripstop for breathability and durability. Underfoot, there’s a new outsole that has D30 shock-absorbing inserts, and uses Fox’s Ultratac rubber.

There are three big differences between the two generations of Union BOA I’ve ridden in, two small, and one big. The first is the lace material difference. I tend to prefer the textile BOA laces as opposed to the steel cables because after a bunch of use, the cable’s mode of failure tends to be wearing through a guide, while the textiles tend to fray and break. It’s easier to replace a lace than a guide, so I’ll take the textile laces, but it’s honestly not a huge deal to me. The second is the D30 insert in the outsole. Honestly, that sounds nice, but it’s not the sort of thing that I really notice riding. These shoes handle impacts fine, but it’s not like they’re game-changingly better than the alternative.

Finally, the most important change is the shift to softer, smaller, lower lace guides recessed into the shoe. These allow the shoe to flex naturally with your foot when walking and pedaling. I found that the big plastic guides caused some big comfort and chafing issues on the old version, to the point where I had hot spots after an hour or so, and was missing skin after half-day rides. The new eyelets are so much less obtrusive and more comfortable. They're a huge upgrade.

Fox Union BOA Flat Performance

There are two metrics to judge flat pedals shoes on: grip, and everything else. In terms of grip, I think Specialized and Five Ten are still winning the battle by a large margin. Specialized’s SlipNot rubber is, in my experience, the tackiest around, with Five Ten’s Stealth right behind it (with worse durability). Then there’s a notable gap to where the rest of the market (Shimano, Leatt, Ride Concepts, etc) are all playing. The Union BOA’s Ultratac rubber isn’t in the same class of grip as Specialized or Five Ten, but it’s still totally adequate, and compares well to every other brand on the market. These shoes grip well enough that I’m happy to take them on any ride, on any trail, which I would hesitate to do with many other shoes. That’s totally adequate and, so far, I’ve been quite impressed with their durability as well.

So the grip is fine, how’s the rest of the shoe? The Union BOA does a good job of threading the needle between sleek clipless-inspired shoes and clunky, super-padded skate-inspired options. It isn’t unnecessarily bulky, and it dries quickly, but it’s got plenty of padding and protection where you need it. I’d classify the flex as medium-stiff, similar to the Specialized 2FO. That means there’s plenty of support and comfort on the pedals, but you can still walk effectively instead of prancing along on too-stiff soles. The Union breathes reasonably well in the summer, and doesn’t feel stiflingly hot, but manages to perform just fine in colder weather too. 

All that to say, the Union is a pleasantly “neutral” shoe that's ready for just about any bike ride. Yeah, when things get really nasty, you’ll want to reach for the “All Weather” version, but for the rest of my rides, I’m quite happy in the regular Union.

For Now

It’s nice when a perfect product drops, but there’s always room for improvement. It’s great to see Fox update the Union BOA Flat in small ways that make it notably better. The result is a solid, do-it-all flat pedal shoe that I’m stoked to keep riding in.

Learn more: Fox