Brooks Glycerin 21 review: Softer ride and changed fit

Brooks Glycerin 21

OUR VERDICT: 82% – GOOD

The Glycerin 21 is a comfortable shoe for everyday miles at easy speeds. It fits shorter and narrower than the Glycerin 20, and has a softer midsole. The outsole has an improved grip but lower durability.

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With 20 different versions behind it, the Brooks Glycerin has had a long and eventful history.

Before oversized Hokas and superfoam midsoles became the norm, models like the Brooks Glycerin and Asics Nimbus were advertised as running shoes that offered the plushest ride and upper. And they did – considering that pre-2010 shoes were mostly based on EVA midsoles (Mind you, Nike Lunarlon was still breaking out) with some kind of cushioning insert.

The original ‘DNA’ insert inside the Brooks Glycerin 9 was a non-Newtonian Gel that absorbed impact forces by turning firmer during landings.

How times have changed. While the Nimbus and Glycerin are still very popular (and cushioned), they are no longer the plushest shoes that money can buy.

The added padding pushes the foot forward by a few mm.

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Brooks hasn’t got the memo yet, and claims the Glycerin 21 has ‘supreme softness’. If we remember correctly, Brooks said the same thing about the firm Brooks Glycerin 20.

While the Brooks Glycerin 21 is softer than the Glycerin 20, it’s not supremely soft when compared to other shoes of its class. For example, it’s firmer than the New Balance 1080V13, Saucony Triumph 22, Puma Magnify Nitro 2, and even the Asics Nimbus 26.

Runners who are familiar with some of these shoes will know they are best used for.

The Brooks Glycerin 21 doesn’t like to be pushed hard; it’s on its best behavior at speeds slower than 5:00 min/km (8 min/mile). The cushioned midsole also keeps the foot comforted and protected during a long run, even though the shoe doesn’t live up to its ‘supreme softness’ advertising.

Here’s why the Glycerin 21 has a noticeably softer ride

Two changes to the midsole make it softer than the previous model.

The Nitrogen-infused DNA Loft has a lower density – and therefore, easier to compress – than the foam on the Glycerin 20. The Glycerin 21 also gets an extra 2 mm of stack height over the 20. When in motion, the foam has a lot more ‘give’ – the foot sinks deeper into the midsole than the firmer G-20.

The step-in comfort hasn’t changed, as Brooks re-uses the same parts from the last model. A blown foam insole with a plush textile footbed and foam lasting add a comfortable layer of squish just under the foot.

The Brooks Ghost 16 recently switched to a DNA Loft material like the Glycerin, but it uses a firmer variant.

The Glycerin 21 fits narrower and shorter than the previous model

The Glycerin fits true-to-size, but barely. The large toe sits closer to the tip of the shoe than the previous model.

The upper also fits narrower, and the bulkier Brooks logos on the sides make the midfoot upper stiffer. As for the toe box, it isn’t shallow and has decent levels of space.

The added padding pushes the foot forward by a few mm.

And why has the fit changed? The heel collar has a higher level of padding than last year’s model, and that pushes the foot forward by a few millimeters. While there is an optional wide sizing available, we doubt if that’s going to influence the slightly shorter fit.

(Note: We haven’t tried the Stealthfit version of the Glycerin, but we assume that it should fit differently (less short) than the standard upper.)

The heel fit is excellent, as the stiff counter and generous padding keep the foot locked in. The 21’s tongue doesn’t have a sleeve, so it slides to the outer side during a run.

The insides aren’t exactly breezy, but it isn’t oven-warm like the Asics Nimbus 26. The mesh does a fair job of ventilation, and we’d say that the Glycerin 21 is a very decent three-season shoe, freezing winters excluded.

This easy-speed cruiser struggles during high-speed runs, intervals

We prefaced this review with what the Brooks Glycerin 21 was good for; a cushioned shoe for unhurried paces.

As long as the shoe isn’t subjected to aggressive speeds, the DNA Loft midsole makes it easy to hold a pace. The thick foam stack is protective and smooth in its cushioning delivery. There’s enough comfort for up to a marathon, so if your target finish time is over 3:45, this shoe will do just fine.

There are a few reasons why it’s hard to coax quick miles out of the Glycerin 21. Runs like intervals, short races, and their kind should be best left to other shoes. For example, the Brooks Hyperion or Hyperion Max (V1) works much better for speed-oriented workouts.

The midsole lacks the firmness – or a rigid component like a plate – to make the loading efficient. The midsole also lacks a rocker for easier roll-offs.

The Glycerin’s lack of high-speed capabilities is certainly not a negative. The Brooks Glycerin 21 simply isn’t that kind of a shoe. But a shoe review should set expectations, and that’s what we’re doing here.

The midsole stability is lower than before

This kind of deformation would be unimaginable on the Glycerin 20.

For lightweight runners with a neutral gait, the softer Glycerin 21 will provide adequate levels of ride support. But if you’re a heavy runner pounding the Glycerin into the road, the midsole deforms far more easily (see picture above) than the Glycerin 19 and 20.

Heavy runners, or runners who severely under or over-pronate will not find the rock-solid stability of the previous model. There’s only so much raised sidewalls and an under-heel cavity can achieve; the G-21’s taller and softer midsole offsets these stability features.

The stiff forefoot takes a few runs to break in

The Brooks Glycerin 21 is stiff right of the box. Even with the spaced-out outsole lugs, the forefoot is inflexible. It will take a few runs (around 30 miles) for the forefoot to ‘loosen up’ and become easier to bend.

It will retain most of the initial stiffness, so don’t expect the midsole to become ultra-flexible over time.

Good for heel strikers, decent for midfoot/forefoot strikers

As far as heel drops go, the Brooks Glycerin 21 sits pretty high up on the scale. The 38 mm (heel) and 28 mm (forefoot) stacks result in a 10 mm heel-to-offset.

Most of the foam is stacked under the rear, so forefoot strikers will get the shorter end of the cushioning stick. However, this doesn’t mean that this shoe won’t work for full-contact landings.

The beveled (rounded) heel edge doesn’t catch the ground, and the 28 mm forefoot stack provides ample cushioning.

The outsole has lower durability but better traction

For this version, Brooks has split the forefoot outsole into several pieces. But the layout isn’t the only change here; the rubber is softer than what was on the G-20.

There’s feedback around reduced durability or accelerated wear and tear on the forefoot outsole as well as the inner rear outsole. The outsole on the outer landing zone is firmer than the rest, and thus more durable.

This isn’t a surprising outcome. A soft rubber compound that doesn’t telescope deeply into the midsole will wear out quicker than a firmer rubber. This takes us back to pre-2016 Brooks running shoes that had an excellent grip but had the tendency to wear down sooner.