Why the Unique Merrell "Hydro Moc" Sandal Is Creating a Buzz Both in the City & the Mountains

There are countless shoes developed with outdoor use in mind that end up being widely worn in urban environments as well.

The American footwear brand Merrell's "Hydro Moc" released in 2019 is the perfect example of a sandal that embodies today's "urban outdoor" style.

Originally designed for river adventures, these sandals also offer true comfort in the city, while their striking design adds an edgy twist to any outfit. How did this amphibia sandal, blending function and design, come to life—and what propelled it to global popularity?

We spoke with Yusuke Tanaka, who oversees marketing at Marubeni Consumer Brands, the official importer and distributor of Merrell in Japan.

A High-Performance Sandal Born for River Walking Activities

"The inspiration for creating the Hydro Moc was the widespread activity of hydro hiking in America," Tanaka explains.

Hydro hiking is a portmanteau of Hydro (water) + Hike, and refers to all activities involving walking in watery landscapes—rivers, wetlands, muddy mountain trails, and more.

"For decades, Merrell has focused on developing amphibious footwear suitable for hydro hiking. This model was created as a sandal to tackle river hikes, where you might wade through shallow water or hop across stones," says Tanaka.

What truly stands out is the truly original design—the silhouette evoking rocky terrain, and the randomly placed openings on the upper create a commanding presence.

"Merrell's core design philosophy is purpose-driven: we start by considering what kind of functionality is needed in a given environment. The shape of this river-hiking sandal is actually inspired by the movement of water flowing over rocks, which can help reduce water resistance."

The openings in the upper have a clear purpose too.

"Even if water enters the sandal, every step pushes it out through these holes, keeping the inside dry and comfortable."

Shoe-like Fit, Thanks to a Sophisticated Last

When you actually put them on, the fit is more like a shoe than a typical sandal.

"Most river-hiking sandals come with straps to hold the foot and instep securely, so you won't lose them in strong water currents. But straps can make them cumbersome to take on and off.

"That's why we chose a slip-on design for this model. It not only makes them easy to put on and take off, but also ensures a closer fit between the upper and the foot—so they're less likely to get swept away by the water," explains Tanaka.

The movable heel strap and the anatomically shaped insole, aligned perfectly with the arch, also enhance fit and comfort.

"When it comes to Merrell slip-on shoes, the best-selling 'Jungle Moc' released in 1998 is especially famous. The reason people still love them is their outstanding fit—so much so, they're called 'mocs you can run in.' That fit comes from Merrell's exceptionally designed lasts.

"Even with outdoor sandals, we're able to leverage the last development expertise honed through years of making the Jungle Moc."

The Hydro Moc features a structure that wraps around the heel like a shoe, but it’s designed not to hinder putting them on or taking them off.

"Even if you step on the heel part while putting them on, the heel is engineered to pop back up once your foot is fully inside the sandal."

Achieving Outstanding Comfort & Sustainability

In 2022, the materials were renewed using sustainable options. The main body features a plant-based biomass material called BLOOM™.

"Due to recent global warming, algae in lakes across the world have multiplied excessively, disturbing ecological balances underwater. In response, technology has been developed to recycle algae as a resource. The body of this model is made with a special EVA foam blended with algae processed into fine chips."

This material offers various environmental benefits, including purifying water by suppressing excessive algae growth and helping achieve carbon neutrality by reducing CO₂ emissions during manufacturing.

"Because it’s made from a one-piece molded EVA, there are no gaps for water to seep in, and thanks to the material's properties, it hardly absorbs water. Even if they get wet or dirty, simply wiping and air-drying in the shade is enough."

While trying them out, I also checked their cushioning. With just the right amount of resilience—it’s impressively cushioned but not overly soft, possessing a pleasant firmness.

"The midsole uses Merrell’s original Float Pro™ foam, developed during the process of creating trail running shoes.

"While the materials and molding method are mostly similar to regular EVA, Merrell fine-tunes the resin and molding process—adjusting heat and pressure—to produce an exclusive EVA foam that excels in lightness, responsiveness, and durability."

When actually walking, I had the sensation that my feet moved forward effortlessly.

"Thanks to excellent bounce-back, energy return during each step increases, allowing for smooth strides. They’re also highly resistant to flattening out, ensuring the cushioning lasts long."

The Float Pro™ foam is also environmentally friendly—it’s made in a zero-waste production process and uses recyclable TPE (thermoplastic elastomer) as its raw material.

The sandals also deliver grip that grabs onto the ground, making them feel like they go beyond typical sandals.

"River hikes can involve walking over wet rocks, so we’ve adopted a three-dimensional oval lug pattern that wraps around the front, back, and sides of the outsole."

A Global Breakout Sparked by Fashion Movements

Although every aspect—from materials to design—was purpose-driven, it was fashion that propelled the Hydro Moc to popularity.

"In 2021, a prominent European influencer stirred up buzz on social media by pairing a black Hydro Moc with all-black, tech-inspired apparel.

"Around that time, Merrell was already getting attention, partly due to the launch of the global premium collection 'Merrell 1TRL,' announced in the previous year. This recognition is considered one reason behind the Hydro Moc's breakout."

Additionally, the chaos of the pandemic era seemed to highlight the popularity of eccentric designs like the "Weird Sandals." The Hydro Moc repeatedly appeared in fashion culture magazines during this period.

Ordinarily, sandals are a summer-centric item, but Hydro Moc smashed the "summer only" stereotype of sandals.

"One fashion magazine featured them for fall and winter styles, suggesting coordination with socks. That article triggered ongoing sales, making Hydro Moc a year-round sandal."

The Hydro Moc is versatile enough for a wide range of scenarios, making it a staple in many situations.

"For activities like mountain hiking that involve tent stays, they're often used as secondary or recovery shoes. On Instagram, you’ll often spot Hydro Mocs hanging from backpacks.

"They're also popular as casual footwear around city streets. Thanks to their light weight and breathability, many wear them barefoot during summer months."

Their functionality as amphibious sandals is especially appreciated at rainy music festivals.

A Game-changer that Transformed the "Autumn/Winter Brand" Image

"Before Hydro Moc arrived, Merrell had long been associated with the 'autumn/winter' season. But with the arrival of this model, wearable year-round, Merrell gained visibility even in the spring and summer seasons."

In recent years, Merrell has achieved record sales across all seasons, largely thanks to the success of this model.

From rivers and mountains to urban jungles, the Hydro Moc is the next-generation urban outdoor sandal, ready to tackle any terrain.