Our verdict

Offering an updated upper that differs from the standard version, the Brooks Glycerin StealthFit 20 is a compelling shoe that gained our admiration. It’s kind of a perfect mix, where softness meets responsiveness, and comfort meets reliability. Daily trainer at the core, it’s a true workhorse that we found to be perfect to cover miles and miles at a relaxed pace, without worrying about tiring our legs.

Pros

  • Responsive midsole
  • Good impact dampening
  • Suitable for recovery days and long distances
  • Stable and smooth ride
  • Extremely breathable
  • Seamless upper
  • Snug, sock-like fit
  • Super comfy and suitable for all day wear
  • Durable outsole and upper construction
  • Great traction, even on wet surfaces

Cons

  • Somewhat firm midsole
  • Needs breaking in
  • Pricey for a daily trainer

Audience verdict

83
Good!

Who should buy

We recommend the Glycerin StealthFit 20 to runners: 

  • Looking for a comfy and protective road shoe
  • Who need a reliable shoe that performs consistently regardless of season
  • In the market for a versatile daily trainer that can do a bit of everything
  • With slightly pronating strides but prefer neutral shoes that feel stable underfoot

Brooks Glycerin Stealthfit 20 1

Who should NOT buy

While the Glycerin StealthFit 20 is capable at high paces, we don’t recommend it as a dedicated speed trainer. For maverick runners with the need, the need for speed, we suggest checking out the ASICS Novablast 3 or the nylon-plated Saucony Endorphin Speed 3. 

The Glycerin StealthFit 20’s midsole is definitely on the firmer side. For runners who prefer more plush cushioning underfoot, we recommend the ASICS Gel Nimbus 25 instead. 

Wide-footed runners might find the Glycerin StealthFit 20 a little too snug, especially when it comes to foot-swelling long distances. The Brooks Launch 10 is a roomier alternative that can go for miles on end.

Brooks Glycerin Stealthfit 20 cut

Breathability

We pumped the Glycerin StealthFit 20 full of smoke to assess how breathable it is. As the video demonstrates, smoke quickly and evenly vents from the shoe; streaming out in clouds from the toebox to the tongue. This earns the Glycerin StealthFit 20 a perfect 5 out of 5 for breathability, making it a great choice for toasty summer runs. 

Compare that to the abysmal performance of the Adidas Runfalcon which is basically a toaster for feet. 

To better understand the shoe’s airflow, we inspected a cross-section of the upper over a light. This, unfortunately, proved fruitless as the light didn’t really shine through any part of the shoe. 

We then turned to our microscope for answers, but what we found only confounded us further. The knit upper is made of layers of dense, tightly woven braids of different materials; thick, fuzzy threads make up the outer layer, while underneath is formed from lighter strands. Still, it doesn’t seem like there are many spaces for heat to escape the shoe. This leads us to believe that the material itself is very porous and breathable.

Brooks Glycerin Stealthfit 20 mc

Brooks Glycerin Stealthfit 20 Breathability
Test results
Glycerin Stealthfit 20 5
Average 3.8
Compared to 209 running shoes
Number of shoes
1
Breathability
5

Durability

Toebox durability

We fired up our Dremel to subject the Glycerin StealthFit 20 to extreme wear and tear. Applying 3.2N of abrasive force spinning at 5K RPM to the toebox turned out much less eventful than expected, with the tool’s grinding element seemingly unable to bite into the material. 

Inspecting the aftermath of the four-second test, we can see that the Dremel did manage to shred a rather large area of the top knit layer. Apart from that, it remains relatively intact as it doesn’t go all the way through the toebox, earning the Glycerin StealthFit 20 a toebox durability score of 3 out of 5. This is a much better performance in this test than the average road shoe, making the Glycerin StealthFit 20 a hardy, battle-ready shoe.

Brooks Glycerin Stealthfit 20 Toebox durability
Test results
Glycerin Stealthfit 20 3
Average 2.3
Compared to 143 running shoes
Number of shoes
1
Toebox durability
5

Heel padding durability

Next to face the Dremel is the heel counter which also managed to stave off our relentless Dremel quite well.

After four seconds of punishment, the Glycerin StealthFit 20 walks away from the test with nothing more than an unsightly scuff on the lining material. As a result, we give the Glycerin StealthFit 20 an admirable heel padding durability score of 4 out of 5.

Brooks Glycerin Stealthfit 20 Heel padding durability

The Under Armour Charged Assert 9 didn't fare nearly as well in the same test

Test results
Glycerin Stealthfit 20 4
Average 3.1
Compared to 139 running shoes
Number of shoes
1
Heel padding durability
5

Outsole hardness

We pressed our durometer against the Glycerin StealthFit 20’s outsole and got a much softer-than-average reading of 75.0 HC. While this level of softness means that the shoe is able to bite into and grip surfaces well, it usually doesn’t bode well for durability. We’ll put that assumption to the test in the next section. 

Brooks Glycerin Stealthfit 20 Outsole hardness
Test results
Glycerin Stealthfit 20 75.0 HC
Average 80.3 HC
We use an average of four tests. The photo shows one of those tests.
Compared to 260 running shoes
Number of shoes
55.5 HC
Outsole hardness
92.8 HC

Outsole durability

Wielding our Dremel for the third and final time, we applied its grinding element to the outsole, this time spinning at 10K RPM for twenty seconds. We expected pure chaos based on the softness of the rubber, but surprisingly our tool only sent small flecks of material flying off the outsole. 

Once the dust had settled, we assessed the damage with our tire gauge and found that we had only sheared off 0.67 mm of rubber from the Glycerin StealthFit 20’s outsole. This is much more durable than the average road shoe, leading us to confidently predict that the Glycerin StealthFit 20 will comfortably see 500 miles of use before any major signs of wear and tear.

Brooks Glycerin Stealthfit 20 Outsole durability
Test results
Glycerin Stealthfit 20 0.7 mm
Average 0.9 mm
Compared to 121 running shoes
Number of shoes
0.0 mm
Outsole wear
2.0 mm

Outsole thickness

At 4.0 mm thick according to our caliper measurements, the Glycerin StealthFit 20’s outsole is slightly thicker than our current lab average. With the performance of the outsole in our previous test, however, we think that the Glycerin StealthFit 20 could easily lose some material in order to shave off some weight without sacrificing durability. 

Brooks Glycerin Stealthfit 20 Outsole thickness
Test results
Glycerin Stealthfit 20 4.0 mm
Average 3.2 mm
Compared to 279 running shoes
Number of shoes
0.0 mm
Outsole thickness
6.6 mm

Weight

Tipping our scale at 9.9 oz (281g), the Glycerin StealthFit 20 is slightly heavier than the average road shoe. Despite this, however, the shoe manages to feel quite light and swift underfoot thanks to its responsive midsole and buttery smooth ride. 

Brooks Glycerin Stealthfit 20 Weight
Test results
Glycerin Stealthfit 20 9.91 oz (281g)
Average 9.35 oz (265g)
Compared to 280 running shoes
Number of shoes
5.26 oz (149g)
Weight
12.56 oz (356g)

Cushioning

Heel stack

The Glycerin StealthFit 20 boasts a massive heel stack that’s 38.8 mm high according to our caliper. This isn’t just more foam underfoot than average, but 4 mm higher than advertised by Brooks.

Brooks Glycerin Stealthfit 20 heel

As such, heel strikers have plenty of foam to really sink into and savor the midsole cushioning despite it being somewhat firm. This makes the Glycerin StealthFit 20 a great choice for long-distance efforts or recovery days where great impact dampening is paramount.

Test results
Glycerin Stealthfit 20 38.8 mm
Average 33.5 mm
Compared to 279 running shoes
Number of shoes
7.6 mm
Heel stack
42.7 mm

Forefoot stack

Moving up to the forefoot, we measured the Glycerin StealthFit 20 to be 26.3 mm thick. This is also thicker than average and affords forefoot strikers similarly well-cushioned landings. 

Brooks Glycerin Stealthfit 20 fore

This lofty stack means that we don’t get much sensation of the road below as we run. For runners who prefer more ground feel from their daily trainer, we suggest checking out the Brooks Hyperion instead.

Test results
Glycerin Stealthfit 20 26.3 mm
Average 24.9 mm
Compared to 279 running shoes
Number of shoes
7.6 mm
Forefoot stack
35.8 mm

Drop

The difference in our stack measurements leaves us with an offset of 12.5 mm. This is quite a bit higher than the 10 mm officially stated by Brooks but still classifies the Glycerin StealthFit 20 as a high-drop shoe. 

Brooks Glycerin Stealthfit 20 drpo

We recommend that forefoot strikers accustomed to shoes with lower heel drops look into the mid-drop Brooks Levitate StealthFit 6 or the low-drop New Balance Fresh Foam X Kaiha Road instead.

Test results
Glycerin Stealthfit 20 12.5 mm
Average 8.6 mm
Compared to 279 running shoes
Number of shoes
-0.8 mm
Drop
16.1 mm

Insole thickness

The Glycerin StealthFit 20’s insole is 5 mm thick according to our caliper measurements which is slightly thicker than our current lab average. This gives us a nicely padded surface within the shoe that complements the midsole cushioning. 

Brooks Glycerin Stealthfit 20 Insole thickness
Test results
Glycerin Stealthfit 20 5.0 mm
Average 4.4 mm
Compared to 275 running shoes
Number of shoes
1.5 mm
Insole thickness
7.3 mm

Midsole softness

Note: a low durometer measurement equals a soft material, whereas a high measurement means it's firm.

We pressed our durometer against the midsole foam and got a reading of 29.3 HA. In spite of this being quite a bit firmer than average, the cushioning feels more balanced than firm underfoot. 

Brooks Glycerin Stealthfit 20 soft

This is thanks to the shoe’s substantial stack which really improves our sense of perceived cushioning as the dense foam compresses during our landings. Apart from being protective, the DNA Loft v3 midsole also feels responsive as it rebounds during toe-off. This makes bounding from one step to the next feel much more effortless, with this efficient energy return helping us gobble up the mile markers during our long-distance runs.

Test results
Glycerin Stealthfit 20 29.3 HA
Average 21.3 HA
We use an average of four tests. The photo shows one of those tests.
Compared to 207 running shoes
Number of shoes
8.5 HA
Midsole softness (soft to firm)
41.5 HA

Difference in midsole softness in cold

To measure how much firmer the midsole becomes in cold conditions, we placed the Glycerin StealthFit 20 in the freezer for twenty minutes. We then took another durometer reading of the midsole foam and got a reading of 33.4N. This is firmer than average and means that while the Glycerin StealthFit 20 will still provide decent protection during winter runs, it certainly won’t feel as forgiving underfoot as in the warmth. 

With only a 14% increase in firmness, the Glycerin StealthFit 20’s midsole is much more consistent than our current lab average. So while it’s certainly on the firm side, the difference in cushioning won’t feel so different between summer and winter runs. 

Brooks Glycerin Stealthfit 20 Midsole softness in cold
Test results
Glycerin Stealthfit 20 14%
Average 25.7%
Compared to 206 running shoes
Number of shoes
0%
Difference in midsole softness in cold
100%

Stability

Lateral stability test

While there is a bit of excessive lateral movement as we shift our weight from side to side in the Glycerin StealthFit 20, it still feels remarkably well-planted for a shoe with such a substantial stack height. 

That being said, runners with pronounced overpronation in their strides should look into more supportive stability trainers like the GTS version of this shoe or the ASICS GT 2000 12 instead. 

Torsional rigidity

We encountered quite a bit of resistance as we attempted to bend and twist the shoe in our hands, leading us to give the Glycerin StealthFit 20 a torsional rigidity score of 4 out of 5. With no plate to be found on the shoe, this stiffness is all thanks to the chunky midsole. This level of rigidity helps to offset the instability of the high stack by providing a level base for well-balanced landing and toe-offs. 

Test results
Glycerin Stealthfit 20 4
Average 3.2
Compared to 258 running shoes
Number of shoes
1
Torsional rigidity
5

Heel counter stiffness

The Glycerin StealthFit 20’s heel counter feels moderately stiff based on our manual probings, earning it a middle-of-the-road score of 3 out of 5. This is comfortable for a daily trainer as it has enough structure to securely hold our heel in place without putting too much pressure on our tendons. 

Test results
Glycerin Stealthfit 20 3
Average 2.7
Compared to 242 running shoes
Number of shoes
1
Heel counter stiffness
5

Midsole width in the forefoot

It’s in this department that the Glycerin StealthFit 20 proves that the fundamentals are key: a wide base is a steady one. With the midsole 118.6 wide at the forefoot, it’s significantly broader than our current lab average. 

Brooks Glycerin Stealthfit 20 midwid

This gives us more than enough platform to ensure extremely stable landings and toe-offs in this shoe while still feeling nimble and agile around corners.

Test results
Glycerin Stealthfit 20 118.6 mm
Average 113.5 mm
Compared to 280 running shoes
Number of shoes
100.5 mm
Midsole width in the forefoot
126.5 mm

Midsole width in the heel

The midsole is just as robust at the heel, measuring 97.2 mm wide according to our caliper. This is much broader than average and means that heel strikers will also enjoy surefooted landings in the Glycerin StealthFit 20. 

Brooks Glycerin Stealthfit 20 Midsole width in the heel
Test results
Glycerin Stealthfit 20 97.2 mm
Average 90.3 mm
Compared to 280 running shoes
Number of shoes
74.9 mm
Midsole width in the heel
106.6 mm

Flexibility

Stiffness

After securing the Glycerin StealthFit 20 to our workbench, we measured the amount of force needed to torque the shoe to 90 degrees. Requiring 30.8N to bend it to the desired point means that the Glycerin StealthFit 20 is about as flexible as average for a road shoe. As such, the shoe is able to bend along with our foot with relative ease which contributes to its overall comfort.  

However, as the Glycerin StealthFit 20’s girthy midsole affects its flexibility, the shoe will feel a little stiffer than that until it's broken in.

Test results
Glycerin Stealthfit 20 30.8N
Average 29.4N
We use an average of four tests. The video shows one of those tests.
Compared to 262 running shoes
Number of shoes
2.2N
Stiffness
94.4N

Difference in stiffness in cold

We also repeated our stiffness test after leaving the shoe in the freezer for twenty minutes. With 32.3N of force now needed to bend the shoe makes it much more flexible than the average road shoe under similar conditions. In fact, it’s barely as if we changed anything at all!

Becoming only 4.9% stiffer in the cold makes the flexibility of the Glycerin StealthFit 20 much more consistent than the average road shoe between warm and cold conditions. This means that the shoe should feel just as forgiving on the foot during harsh and frigid winter runs as it does during a warm summer jog. 

Test results
Glycerin Stealthfit 20 4.9%
Average 37%
Compared to 262 running shoes
Number of shoes
0%
Difference in stiffness in cold
148%

Grip / Traction

The intricate tread pattern on the Glycerin StealthFit 20’s outsole gave us great traction on the road during our test runs. Even a section of slick cobblestones soaked by a nearby sprinkler close to our lab wasn’t enough to catch us slipping in this shoe. As such, we have no fear of being caught in a sudden downpour in the Glycerin StealthFit 20.

Brooks Glycerin Stealthfit 20 grip

Size and fit

Toebox width at the widest part

We measured the Glycerin StealthFit 20’s toebox with our caliper to be 96.5 mm wide at its widest point. This is narrower than our current lab average and means that the Glycerin StealthFit 20 is suitable for those with narrow to normal feet. 

Brooks Glycerin Stealthfit 20 widest

However, this makes it a less-than-ideal choice for runners with wide feet who will be prone to hotspots or even blisters in this shoe, especially as the feet swell toward the end of longer runs. We recommend the Brooks Launch 10 or the Adidas Adizero SL as roomier alternatives.

Test results
Glycerin Stealthfit 20 96.5 mm
Average 98.3 mm
Compared to 280 running shoes
Number of shoes
89.5 mm
Toebox width at the widest part
109.1 mm

Toebox width at the big toe

The Glycerin StealthFit 20’s toebox tapers to 77.6 mm wide in the area around the big toe. This is slightly wider than our current lab average which gives us enough room for our toes to splay out naturally during landings. 

Brooks Glycerin Stealthfit 20 Toebox width at the big toe
Test results
Glycerin Stealthfit 20 77.6 mm
Average 78.1 mm
Compared to 154 running shoes
Number of shoes
60.4 mm
Toebox width at the big toe
92.5 mm

Tongue: gusset type

The Glycerin StealthFit 20’s upper is a seamless construction that has a sock-like fit that’s snug and comfy. What’s more, the unique lacing system that employs a stretchy string instead of traditional lace loops locks the shoe down in a way that feels like it molds around our foot.

Brooks Glycerin Stealthfit 20 Tongue: gusset type
Test results
Glycerin Stealthfit 20 Sock like

Comfort

Tongue padding

The single-piece construction of the Glycerin StealthFit 20’s upper means that there is no tongue to speak of. Measuring the material that runs across the instep with our caliper reveals it to be a mere 1.5 mm thick. This is much less thick than our current lab average and means that the laces did feel quite apparent across our instep during our test runs. 

Brooks Glycerin Stealthfit 20 tongue

For those who prefer a more traditional fit with a padded tongue, we recommend the standard version of the shoe, the Glycerin 20.

Test results
Glycerin Stealthfit 20 1.5 mm
Average 5.6 mm
Compared to 277 running shoes
Number of shoes
0.5 mm
Tongue padding
14.2 mm

Heel tab

There’s a finger loop on the Glycerin StealthFit 20’s heel counter that makes it easy to slide the shoe on and off. 

Brooks Glycerin Stealthfit 20 Heel tab
Test results
Glycerin Stealthfit 20 Finger loop

Removable insole

The Glycerin StealthFit 20’s insole is fully removable, making the shoe compatible with custom orthotics if necessary. 

Test results
Glycerin Stealthfit 20 Yes

Misc

Reflective elements

With no reflective elements to speak of, the Glycerin StealthFit 20 does nothing for nighttime visibility. We, therefore, recommend that runners use additional high-vis gear when burning the midnight oil in this shoe. 

Brooks Glycerin Stealthfit 20 Reflective elements
Test results
Glycerin Stealthfit 20 No