Earth Runners Ion Sync Tolos Review

Overview
The Ion Sync Tolos is Earth Runners’ first closed-toe offering, combining their signature minimalist philosophy with a flexible, athletic build. Designed for those who want a grounded experience year-round, the Tolos offers barefoot enthusiasts a true zero-drop feel, full toe splay, and Earth Runners’ unique grounding technology in a sleek, city-ready silhouette.

From the Manufacturer
Experience unparalleled connection through your entire gait cycle with our most advanced grounding shoe yet.

We’re thrilled to announce the launch of our first barefoot sneaker: iON SYNC® Tolos Shoes.

We've equipped Tolos barefoot shoes with our groundbreaking iON SYNC® Earthing Plugs to offer a shoe designed for biohackers, nature lovers, and rewilding enthusiasts alike.

Our iON SYNC® Earthing Plugs have been years in the making—a highly durable and conductive innovation that replicates the barefoot experience like never before. Integrated seamlessly into the soles of TOLOS, they provide an unmatched grounding experience to help balance your body’s natural energy.

Weight
7.4 oz (mens size 10.5)

Stack Height
6.5mm total stack (per manufacturer)

Zero Drop
Yes

Barefoot Scale
True zero drop with a low-to-the-ground profile. Firm underfoot with enough give to soften hard surfaces. Excellent proprioception for a closed-toe shoe.

Ideal Uses

• Everyday casual wear
• Urban walking
• Travel
• Road running

Pros

• Extremely flexible and foot-conforming
• Toe box encourages natural foot splay
• Excellent ground feel for a closed shoe
• Lightweight
• Machine washable
• Vegan

Cons

• Earthing plug can be felt when barefoot and affects waterproofing
• Insole is not meant to be removable

Sizing
The footbed is shaped to match the foot’s natural contours, with plenty of room for toe splay and natural arch behavior. Earth Runners includes helpful sizing advice on their product page, including specific measurements, though a printable sizing template would be a helpful addition.

Zero drop shoes are designed so that the heel and forefoot sit at the same height, creating a flat sole from back to front. This setup replicates the natural alignment of the foot when walking or running barefoot, encouraging a more neutral posture and gait by keeping the heel and toes level with each other.

Sole
The Ion Sync Tolos fits true to size and features a wide toe box that should accommodate most foot shapes comfortably. While I believe Earth Runners may brand all of their closed-toe shoes under the "Ion Sync" name, for simplicity’s sake, I’ll refer to this particular model as the Tolos for the remainder of this review.

As someone who loved Earth Runners’ Elemental sandals—especially for their blend of simplicity, durability, and excellent groundfeel—I was genuinely excited to see the brand venture into closed-toe shoes with the Ion Sync Tolos. The Elementals had become a staple for me, largely due to the Vibram Gumlite sole, which masterfully balanced firmness and cushioning, with just enough lug definition to handle both trails and pavement with ease.

So when the Tolos dropped, I had pretty high expectations. The standout feature here is the proprietary iON SYNC composite sole, developed in collaboration with a high-end materials company known for working with tech giants like Tesla and Apple. That certainly sounds promising on paper, but for me, it’s all about how the sole actually feels and performs during real-world use.

Compared to the Gumlite outsole in the Elementals, the Tolos’ sole feels softer, more flexible, and noticeably gummier underfoot. The tread pattern is smoother and less aggressive, signaling a design more focused on urban or casual wear rather than rugged outdoor terrain. The total stack height clocks in at 8.5mm—3.5mm of outsole rubber paired with a 5mm foam insole—keeping the shoe firmly in minimalist territory. Interestingly, that makes the Tolos feel even more grounded than the thinnest Elemental sandals, which use a slightly thicker 7.5mm rubber sole.

One surprise I encountered was the insole situation. My usual habit with minimalist shoes is to remove the insole to maximize groundfeel and create more interior space. But here, the earthing plug runs right through the insole, anchoring it firmly in place. The plug is a small mushroom-shaped nub that’s wider than the hole in the insole it passes through, so once you remove the insole, reinserting it is nearly impossible without damaging or stretching the foam. I learned this the hard way after instinctively pulling out the insole before my first run.

Normally, removable insoles offer some nice customization—you can keep them in for a snugger fit and a bit more cushion or take them out for a roomier, more sensitive underfoot experience. Unfortunately, that flexibility is essentially off the table here unless you’re okay with some permanent modification.

Despite this, the Tolos still delivers a very respectable barefoot feel for a closed-toe shoe. It’s flexible both longitudinally and torsionally, and the grip holds up well on sidewalks, gym floors, and packed dirt trails. That said, I do wonder why Earth Runners chose to move away from Vibram. The Gumlite compound in their Elemental sandals offered an excellent trifecta of traction, durability, and comfort, and it feels like it could’ve elevated the Tolos even further. The iON SYNC sole works well enough for everyday use, but for those coming from the Elementals, it’s a definite shift in both feel and purpose.

The gummier, more pliable sole seems to bring the Tolos closer in feel to shoes like Feelground, which leans heavily into the lifestyle segment. Earth Runners, on the other hand, have historically been known for do-it-all sandals that bridge casual and rugged use seamlessly. So I’m left wondering if Vibram’s Gumlite might have been a better fit to maintain that all-terrain, tough-as-nails reputation, or if Earth Runners are intentionally steering the Tolos toward a softer, more lifestyle-oriented niche.

As someone who typically runs barefoot, I’m pretty sensitive to anything that interrupts the natural feel underfoot—and I can definitely feel the earthing plug at the bottom of the Tolos unless I keep the insole in. It’s not painful, but it’s noticeable enough to be a distraction, especially during longer wear or more dynamic movement. I do wonder if there’s a way to redesign the plug to sit flatter against the sole, or perhaps integrate it higher up in the shoe’s construction—maybe embedded within the midsole or footbed layer.

I fully respect that grounding is central to Earth Runners’ philosophy, and I’m not suggesting they remove that feature—it’s part of what makes their footwear unique. That said, in their sandals, the plug is cleverly built into the toe post, where it’s functionally invisible and doesn’t interfere with footstrike. With a closed-toe shoe, I imagine it’s more complicated, but I can’t help thinking there might be a more ergonomic or discreet way to maintain the earthing connection without compromising that smooth, barefoot-like experience.

Earth Runners are among my go-to sandals, so I was naturally curious how their approach would translate into a closed-toe shoe. I’ve always appreciated their minimalist construction, durable materials, and strong groundfeel—elements that don’t always carry over cleanly into shoes. Moving from sandals to sneakers often means sacrificing some of that raw connection to the ground, so I came into the Tolos with both interest and a bit of skepticism.

Running in the Tolos, though, turned out to be a pleasant surprise. I had expected them to lean more heavily toward casual, everyday wear, but they held up well during short runs and sprints. The outsole is flexible, the upper is light and unrestrictive, and the shoe overall moves with your foot in a way that supports natural mechanics. Groundfeel is preserved better than I expected—there’s enough padding for comfort, but not so much that it dulls your awareness of the terrain.

What stood out most during runs was the balance: the forefoot has enough width and give for natural toe splay, the heel stays put without rubbing or slipping, and the lack of rigid structure gives your foot the freedom to work without feeling sloppy. I wouldn’t personally take them on high-mileage road runs or technical trails—the sole isn’t really built for that—but for barefoot-style runners who prioritize feel and feedback, the Tolos get a lot right.

Traction is adequate for urban and park settings: pavement, grass, hard-packed dirt. I wouldn’t push it on wet roots or steep loose gravel, but for everyday terrain, it’s solid. The fit is close but not constricting, and the inner bootie-style construction adds comfort without friction points. I wore them without socks and didn’t run into any issues with hotspots or chafing.

For experienced barefoot runners, the Tolos may feel more capable than they first appear. They straddle that line between laid-back sneaker and minimalist trainer—maybe not your next race-day shoe, but certainly something you can run in when you feel like it, without needing to change into anything else.

Materials
I really appreciate how the interior of the Tolos looks thoughtfully finished and complete—even if you were to remove the insole (though, as I mentioned earlier, the insole isn’t really designed to come out). The materials inside feel lightweight without ever crossing into feeling cheap, and the overall finish is polished without feeling overly manufactured or sterile.

The upper is made from a thin, breathable polymesh that fits snugly around the foot. I absolutely love the texture—it reminds me of sailcloth watch straps, which gives it a subtle yet interesting visual character. Designed for maximum mobility, the upper bends and flexes easily with your foot, offering almost slipper-like comfort thanks to its integrated “tongueless” construction.

The shoe’s build feels like a mesh sock stitched inside a sturdier sock, with the inner layer providing ventilation around the tongue area, while the outer layer is less breathable but adds durability. This dual-layer approach avoids stiff overlays and excess bulk, focusing on a seamless connection between foot and shoe.

Materials and details reinforce a sleek, futuristic lightweight aesthetic—like the fabric eyelets that hold the rounded laces. That said, I did notice a few exposed foam edges around the outer shell where it was cut; these might benefit from being sealed or finished more carefully to give an even more refined appearance.

Protection and structure mainly come from the color-matched toe and heel caps, which guard against scuffing and wear. Aside from these, the shoe remains flexible and fluid in shape. There’s also a good amount of padded cushioning around the collar, plus a heel loop that makes slipping the shoe on easier.

Aesthetics
The Tolos are among the better-looking minimalist shoes out there. They don’t broadcast their barefoot roots loudly—which is a plus for anyone seeking minimalist function wrapped in a more conventional, wearable style. The all-black colorway is especially versatile, pairing effortlessly with everything from joggers to jeans. The silhouette strikes a nice balance, hinting at light trail-runner performance without tipping into overtly technical or bulky territory. They look fast and sleek, even though they seem designed more for casual, everyday wear. Earth Runners managed to nail a futuristic vibe that honors barefoot design principles without veering into the “clownshoe” territory that minimalist shoes sometimes fall into.

There’s a subtle punchiness to the design—a sharpness in the clean lines and smooth curves that give the shoe energy without feeling overdone. The low-profile shape and streamlined upper lend a sense of motion, making them appear ready to move quickly even in laid-back settings. This understated confidence means they fit seamlessly into both urban environments and more active pursuits, striking a nice middle ground between function and style. Overall, the Tolos deliver minimalist performance with an unexpectedly stylish edge that’s rare to find in this category.

Future Improvements
For future iterations, it would be interesting to see a slightly more aggressive version of the Tolos —something with a water-resistant upper. Obviously, I would want to see the return of Gumlite, but at least a tread design that gives more traction, without sacrificing that good groundfeel.

Summary
The Ion Sync Tolos is Earth Runners’ first closed-toe shoe, designed to extend their minimalist, grounding-focused philosophy into a sneaker format. It features a zero-drop sole, wide toe box, and flexible construction, making it a solid option for barefoot shoe wearers looking for something suited to daily use in urban environments. Ground feel is strong for a closed-toe shoe, and the overall build is lightweight and breathable.

The proprietary iON SYNC® Earthing Plug adds a unique feature aimed at maintaining electrical grounding, though it can be felt underfoot and limits insole customization. The sole is softer and more casual in focus than Earth Runners’ sandals, with a smooth tread that works well on pavement and light trails but isn’t built for rugged terrain or wet conditions.

Fit is comfortable and accommodating for natural foot movement, with good flexibility and a low profile. Aesthetically, the Tolos avoids the bulky look common in minimalist footwear and offers a clean, versatile design. Some finishing details could be improved, and a future version with better weather resistance or modular components could broaden its appeal. As it stands, the Tolos is a thoughtful, if not perfect, addition to the barefoot shoe space—particularly for those already familiar with Earth Runners’ sandals.