Which is lighter, the Brooks Glycerin 20 or the Glycerin 21?

The Glycerin 21, by 0.7 oz in a men's US 9 (9.8 oz vs 10.5 oz).

Do the Brooks Glycerin 20 and Glycerin 21 come in the same widths?

Yes. Both run in D, 2E for men's sizes, so a width that fit in the Glycerin 20 carries over to the Glycerin 21.

How do the stack heights compare?

34 mm heel and 24 mm forefoot on the Brooks Glycerin 20, against 38 mm and 28 mm on the Glycerin 21. That is 4 mm more under the heel and 4 mm more under the forefoot. See the stack height note in the table above: the published figures changed convention mid-lineage.

Is the Glycerin 21 still the newest Glycerin?

No. The Glycerin 22 replaced it in 2025, so the Glycerin 21 now sells as an older model and usually below its $160 list price.

Brooks Glycerin 20 vs Glycerin 21

Updated August 3, 2026. Specs are men's US 9.

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Refined, same shoe

THE SHORT ANSWER

Whichever your size still exists in. The Glycerin 20 is discontinued at retail, so remaining pairs sell against a thinning size run, while the Glycerin 21 has a full one.

Brooks Glycerin 20Sizes running outMen's at Amazon Women's
Brooks Glycerin 21Men's at Amazon Women's

Availability last checked Aug 3, 2026. Prices and stock change without notice.

Glycerin 20 · 2022

Glycerin 21 · 2023

Every spec, side by side

Spec	Glycerin 20	Glycerin 21
FIT AND WEIGHT
Weight	10.5 oz	9.8 oz
	Official and lab figures agree on the 21. Running Warehouse advertised it as almost an ounce lighter than the 20; the exact gap depends on which of the 20's disputed weights you believe.
Widths	D, 2E	D, 2E
Upper	Engineered mesh (StealthFit knit variant also offered)	Engineered warp knit
	Plusher, warmer, with a much stiffer heel counter. The plush collar cost some lockdown.
CUSHIONING GEOMETRY
Heel stack	34 mm	38 mm
	Brooks marketing claimed only 2 mm more foam, and RunRepeat's calipers back that up: the 20 and 21 measured nearly identical at the heel (37.1 vs 37.2 mm), with about 2 mm more up front. Most of the quoted jump is quoting convention, not new foam.
Forefoot stack	24 mm	28 mm
Drop	10 mm	10 mm
MATERIALS
Midsole	Nitrogen-infused DNA Loft v3	Nitrogen-infused DNA Loft v3
VALUE
List price at launch	$160	$160
OTHER CHANGES
Outsole	Standard rubber	RoadTack rubber
	New, more durable compound.

Weighing whether to switch at all, rather than which of these two to buy? What replaced the Brooks Glycerin 20 covers the verdict on the update, what loyalists made of it, and the closest alternatives from other brands.

Buy the Glycerin 20

Sizes running out

Discontinued at retail. Amazon carries what remains, so treat an in-stock size as a closing window, and expect prices to swing.

Men's: Check remaining stock Women's: Check remaining stock

Availability last checked Aug 3, 2026.

Buy the Glycerin 21

Stocked at Amazon

Men's: Check price at Amazon Women's: Check remaining stock

Availability last checked Aug 3, 2026.

Questions runners ask

Which is lighter, the Brooks Glycerin 20 or the Glycerin 21?: The Glycerin 21, by 0.7 oz in a men's US 9 (9.8 oz vs 10.5 oz).
Do the Brooks Glycerin 20 and Glycerin 21 come in the same widths?: Yes. Both run in D, 2E for men's sizes, so a width that fit in the Glycerin 20 carries over to the Glycerin 21.
How do the stack heights compare?: 34 mm heel and 24 mm forefoot on the Brooks Glycerin 20, against 38 mm and 28 mm on the Glycerin 21. That is 4 mm more under the heel and 4 mm more under the forefoot. See the stack height note in the table above: the published figures changed convention mid-lineage.
Is the Glycerin 21 still the newest Glycerin?: No. The Glycerin 22 replaced it in 2025, so the Glycerin 21 now sells as an older model and usually below its $160 list price.