A Big List of Fastpacking Packs
Like most outdoor sports, Fastpacking has developed enough to have a variety of specific gear to make outings more comfortable and enjoyable.
For those of us with a background of backpacking and camping, starting to fastpack doesn’t really require any more gear (often requiring less) and in some ways is more of a mentality shift that anything.
The type of pack you use does make a difference in terms of comfort, storage, and gear accessibility with fastpackers tending to utilize either lightweight frameless packs or running vest-style packs.
While you can technically use any size pack for factpacking, a capacity between 20 liters and 40 liters seems to be the range most fall within. Below 20 liters can be useful for quite specific trips in warmer weather or paired with a belt pack and larger than 40 liters would likely be too heavy once packed to have the chance for any running.
This range has been the sweet spot with my packs being the Ultimate Direction Fastpack 20 and an older Gossamer Gear Kumo 36 (the new fastpacking version looks appealing). My primary pack factors are the fit/comfort, internal/exterior storage, water storage, and the amount of bounce.
I do plan to look more comprehensively at individual packs as time goes on, but for now I’ve created a starter list of packs to consider in order of capacity.

Ultimate Direction
Fastpack 20
This lightweight Fastpack 20 fits like a vest with water bottles up front, but distributes weight like a pack. We gave it an upgrade with Infiknit™ and FastFlow technology to increase the backpanel’s breathability and moisture wicking. This do-it-all pack also has plenty of dedicated external storage, a roll-top opening and a full-side external zipper for easy access to anything inside.
https://ultimatedirection.com/fastpack-20/

Montane
Montane Gecko VP20
The Montane Gecko Vest Pack 20L + is a running pack built to be worn, not carried. This ergonomically fitted, body-hugging hydration vest pack is as secure as a Gecko! An unrivaled large load-carrying construction combines together with a multitude of storage options for all your running essentials, enabling easy access whilst on the move and the ability to carry more – perfect for those planning long days out on the trail.
https://us.montane.com/collections/vest-running-packs/products/montane-gecko-vp-20

WAA
Ultra Bag 20l
The Ultra Bag 20L us an ultra-complete backpack, full of innovative features, comfortable, light and resistant. Since its creation, the Ultra Bag 20L has continued to grow thanks to the feedback of those who have put it to the test in their most extreme adventures.
https://www.waa-ultra.com/en/ultrabag-20l.html

Raidlight
Legend 24L Trail pack
The Legend 24L has ergonomic shoulder straps and padded back allow you to carry additional weight in comfort compared to our race vests. A multitude of loops, straps and compression/overload cord allows to load up additional items on the outside of the pack.
https://raidlight.com/en/products/sac-a-dos-de-trail-activ-legend-24l

Raidlight
Ultralight 24L Trail Running Vest
The Ultralight 24L Trail Running Vest has a zipped roll top closure main pocket. The adjustable Freelock micrometric buckles ensure a perfect fit, while the chest strap fastening system adds extra security. The backpack has three zipped pockets, a water-repellent 1,000 Schmerber 20L zipped main back pocket compatible with a hydration system, and a rear pole holder system.
https://raidlight.com/en/products/sac-a-dos-trail-ultralight-24-30-made-in-france

Kailas
Ultra Gobi Trail Running Backpack 20+5L
The Kailas Ultra Gobi Trail Running Backpack 20+5L is designed for comfort and stability during your outdoor adventures. With multi-layer foam and air channels, the system improves airflow and reduces discomfort. The 3-point shoulder straps and ergonomic hip belt are adjustable for a perfect fit. Featuring a full mesh back for breathability, large capacity for all your gear, and dual pockets for your phone, water bottle, and snacks.
https://kailasgear.com/collections/packs/products/ultra-gobi-trail-running-backpack-20-5l

Salomon
XA 25 Set
Designed with durable, weather-resistant, quick-drying fabrics and a smart roll-top compression system, the XA 25 gives you easy access to essentials like hydration and 25l of storage ideal for longer outings and expeditions. The removeable belt provides extra support and comfort.
https://www.salomon.com/en-int/shop-int/product/xa-25-lc12223.html

Ultimate Direction
Fastpack 30
This lightweight Fastpack 30 allows you to move fast in the backcountry with a durable design that checks all the feature boxes. True to our roots, it uniquely fits like a vest with water bottles up front, but distributes weight like a pack. This do-it-all pack also has plenty of dedicated external storage, a roll-top opening and a full-side external zipper for easy access to anything inside.
https://ultimatedirection.com/fastpack-30/

Vaude
Trail Spacer 28
Fits perfectly – the Trail Spacer 28 sports backpack for motion-intensive hiking trips in the mountains! Thanks to the vest-like suspension system made from a comfortable and extremely durable knitted material, the pack has a comfortable, close fit on your back.
https://www.vaude.com/Trail-Spacer-28-Lightweight-backpack

Gossamer Gear
Fast Kumo 36 Fastpack
The Fast Kumo is a new spin on a Gossamer Gear classic. This pack has been re-designed with a vest- like fit and easy access storage to keep up with you at your fastest speeds. This fastpack is designed to be worn higher and tighter than our original Kumo.
https://www.gossamergear.com/products/fast-kumo

Ultimate Direction
Fastpack 40
This lightweight Fastpack 40 has an optimal weight-to-capacity ratio for longer adventures over rugged terrain so you can move fast in the backcountry. True to our roots, it uniquely fits like a vest with water bottles up front, but distributes weight like a pack. This do-it-all pack also has plenty of dedicated external storage, a roll-top opening and a full-side external zipper for easy access to anything inside.