Brooks Glycerin 21 Review

Are we the only ones who can’t help but hear Gavin Rossdale’s raw, gravelly voice in our heads, urging us to not “let the days go by,” everytime we think about the Brooks Glycerin? Whether or not you’re a fan of the English rock band, music enthusiasts and runners alike can take comfort in the supremely soft cushioning of the Brooks Glycerin 21.

The Brooks Glycerin has always been known for its luxuriously plush midsole, but Brooks designers upped the ante this year with an added two millimeters of DNA Loft v3 foam underfoot, which we’ll talk more about below.

The Glycerin 21 comes in four styles: the Brooks Glycerin 21, the Brooks Glycerin GTS 21, the Brooks Glycerin Stealthfit 21 and the Brooks Glycerin Stealthfit GTS 21. But what do all these names mean? GTS stands for go-to support, and indicates that the shoe has built-in support mechanisms to provide stability for your stride. Stealthfit indicates the shoe has a one-piece, flat-knit upper that provides a different type of fit and feel than the traditional upper used in other styles of the Glycerin.

For this review, we'll stick to the Glycerin 21, which is the style Fleet Feet reviewers tested and just happens to be one of our bestselling Brooks running shoes. The revamped Glycerin line will be available on February 1, 2024.

The big story regarding the previous version of the Brooks Glycerin was their newly formulated DNA Loft v3 foam. This innovative midsole foam is injected with nitrogen, which then turns from a liquid to a gas. So, you’re quite literally running on air! This formula makes DNA Loft v3 foam lighter and more durable than traditional EVA foams.

The Glycerin 20 was a big success, but this latest version may be the best Glycerin yet.

Not only did Brooks add two millimeters of extra midsole foam, they widened the base of the shoe to keep your foot stable and centered on top of the midsole.

“We’ve also continued to refine what we call the ‘dome shapes’ on the sidewalls,” says Dave Patterson from Brooks Running. “These shapes control how the shoe compresses as you run, maximizing the cushioning of the midsole as you land and takeoff.”

The result? A super cushioned trainer that offers an ultra plush ride with just a touch of energy return.

“Running in this shoe reminds me of jumping on a bed, with the same fun factor involved,” says Mandy. “It was plush and comfortable with just a bit of bounce back. I definitely felt more cushion in this shoe than in previous versions of the Glycerin.”

The “bounce-back” sensation Mandy references is something we like to call a shoe’s responsiveness, and other reviewers noticed it too.

While I’ve found most versions of the Glycerin much too soft to offer the responsiveness I like in a trainer, Brooks found the sweet spot with the Glycerin 21 – it provides a luxurious, soft step-in feel with just enough bounce underfoot to feel light on your feet,” says Ashley.

However, some reviewers still think the Glycerin is too soft to feel responsive, but that doesn’t mean they didn’t enjoy some easy-paced miles in this shoe.

“Halfway through my 6-mile run to the Chicago lakefront and back, everything in the Glycerin 21 really started to come together,” says Max. “The uber-plush upper, combined with the soft DNA Loft V3 foam, creates one of the most comfortable all-around running experiences I’ve had all year–although I certainly didn’t feel fast in it.”

The Glycerin 21 is rounded out with Brooks’ new RoadTack outsole, designed to be lighter and more durable than the previous outsole material. Could this be the magic formula Brooks used to add midsole foam while simultaneously shaving weight? Or is it the new, engineered warp-knit upper that dropped weight from the previous model?

While Brooks’ new, engineered warp-knit upper may sound like something out of a sci-fi movie, it fits and feels like a classic Brooks upper. The warp-knit material provides extra breathability and added structure around the midfoot of the shoe for a snug, secure fit.

“I think Brooks fans love their shoes because they are consistent in their fit and feel,” says Kate. “For the most part, Brooks doesn’t tend to make big changes to their bestsellers––just small refinements. The Glycerin 21 follows that trend of consistency. It keeps that classic premium upper with plush elements that dial in the comfort. It’s got a thick, padded tongue that comes up nice and high, and a cushy heel collar. The toe box is roomy and the upper is breathable. The laces are long, which gives you plenty of lace to work with if you snug up your shoe with the marathon loop.”

While the heel collar is cushy, as Kate describes, it also has a fair amount of structure to it which creates a solid, locked-in fit.

Overall, reviewers with all different foot shapes enjoyed the fit of the Glycerin 21.

“The Glycerin 21 feels like a nice hug around my foot,” says Travis. “I really enjoyed the knit material in the forefoot–it makes the shoe feel breathable, light, and accommodating. I am not usually a big fan of plush tongues but this one hit in all the right places without feeling intrusive. Plus, the stretchy laces helped me lock in the fit even more.”

Longtime Glycerin fans can breathe easy–the Glycerin 21 feels remarkably similar to the Glycerin 20, with a few tweaks to improve the fit and feel.

The extra two millimeters of midsole foam make for a softer, more cushioned ride, following the industry trend of midsoles growing taller and taller. But fear not, the added height doesn’t make the shoe any less stable. A wide base creates a sturdy platform for landings and takeoffs.

The warp-knit upper is new, but reviewers thought it offered the same classic Brooks feel.

“The fit of these shoes is classic Brooks–roomy in the toe box, snug in the midfoot and locked down in the heel,” says Caroline. “There is a bit more structure to the heel collar than other comparable models, which makes this a good choice for runners who like a secure, stable feeling. Overall, Brooks nailed this upper–as they usually do.”

The new RoadTack outsole adds grip and durability for wet roads and slick sidewalks.

We took a look at some comparable models to see how they stack up against the Brooks Glycerin 21. Here’s what we found:

Fleet Feet reviewers put the Brooks Glycerin 21 in the highly cushioned, neutral daily trainer category where it fits in with the Saucony Triumph 21 and the ASICS GEL-Nimbus 25. While the Glycerin 21 doesn’t appear to be quite as cushioned as the other two shoes, these differences can be accounted for by the different ways in which manufacturers measure stack height.

Brooks measures their midsole height as a separate unit that doesn’t include the outsole. According to them, the total stack height (including the outsole) is 31 millimeters in the heel and 21 in the forefoot, placing it more in line with the Triumph and Nimbus.

Reviewers found the Glycerin 21 to feel similar to the Triumph 21 in terms of soft-to-firm ratio. While the FF BLAST PLUS ECO foam used in the ASICS GEL-Nimbus 25 feels slightly softer, the Glycerin 21 is a great choice because the ever-so-slight firmness in the DNA Loft v3 makes it more versatile for different types of runs.

At the end of the day, the Brooks Glycerin 21 shines as a highly cushioned, neutral daily trainer for easy-to-medium paced runs. But the nitrogen-infused DNA Loft v3 foam provides a balanced blend of soft and responsive–depending on which reviewer you ask–that can be used for faster runs, too.

“The Brooks Glycerin 21 is a great shoe for neutral runners who like a lot of underfoot cushioning, but don’t want a squishy shoe that bounces too much underneath them,” says Caroline.

“I would recommend the Glycerin 21 for someone looking for a more cushioned daily training shoe,” Travis says. “It has a great base of support, and it’s cushioned while remaining light and bouncy. As a part of a shoe rotation, it makes a great easy or recovery day shoe. Also, I would highly recommend this for walkers or anyone working on their feet all day.”

The Glycerin 21 is available in both standard width and wide width (D for women, 2E for men), so, if you like the underfoot feel, chances are good you can find your perfect fit.