Sierra Designs Flex Hike Day Pack Review

Do you go on a variety of short adventures with different gear needs? Have you ever had trouble finding the perfect size for a day pack because you don’t want to compromise? The Sierra Designs Flex Hike Pack solves these problems for you. With its innovative expanding gusset that expands the pack from 20L to 30L, it is the perfect choice for any day venture you could imagine. Take it on a short stroll in the park or a summit attempt. It also has all the features you’d want in a day pack, including hipbelt pockets, a top zippered pocket, a hydration bladder sleeve, and more.

Sierra Designs Flex Hike Day Pack At a Glance

  • MSRP: $124.95
  • Capacity: 20-30L / 1220-1831 in3
  • Weight: 1 lbs 14 oz  / 0.85 kg
  • Optimal Carry Weight: 10-25 lbs / 4.5-11 kg
  • Material: 100D Nylon Honeycomb, 420D Oxford
  • Torso Fit: One Size
  • Waist Belt Size: 28″ – 52″ / 71 – 132 cm

Intended Use

This pack’s main use would be for day hikes or possibly a short overnight backpack. It’s designed to expand  to accommodate short jaunts or all-day missions; the bottom line is that it is made for variety.

Circumstances of Review

I took this pack on a handful of day hikes of varying length, between 2 and 10 miles. I’ve taken the pack ski touring as well, and it came with me on a weekend trip through the airport carrying all the clothes and gear I needed for three days.

Sierra Designs Flex Hike Day Pack Featuressierra designs flex hike day pack

Expandable volume: The pack includes an expandable gusset to change the volume of the pack from 20L up to 30L. I loved the functionality of the feature, and it was easy to adjust.

Dual adjusting shoulder straps: You can adjust the torso size to fit just about anyone with the shoulder straps. It’s easy to do and adds flexibility. You can share the pack with your friends too! I had no trouble making the pack smaller for my shorter torso.

2 stretch mesh side pockets: The mesh on the side pockets is strong to hold up to abuse and just stretchy enough to hold your water bottles but also keep them in place. I’ve used it to carry Nalgene and Smartwater bottles, and both stayed in and were easily accessible without taking the pack off.

Mesh pockets on waist belt: Perfect for snacks or sunscreen! I was a bit nervous when I first saw these pockets and how they don’t zip but I was impressed with how well everything stayed in.

Small Stash Pocket & Front hidden zippered pocket: I always look for a zippered pocket to throw my keys/wallet in for a day hike. The stack pocket is easily accessible and perfect for small items that might otherwise get lost in the pack. In addition to the stack pocket, there are also two hidden pockets on the front of the pack. They’re so well hidden that I truthfully didn’t even notice them at first. It’s a great place to store something you want to keep safe or other small items.

U-shaped top access: The U-shaped entry to the pack was a feature I really enjoyed. It keeps the pack together well as you’re loading it up with all your gear or trying to find something without everything else falling out.

Hydration pack ready: The pack comes with a sleeve for a hydration bladder so if you that like to drink your water from a straw are good to go! I also used this sleeve to hold my laptop for a weekend trip away that included hiking and working, although there is no cushioning for protection if you go that route as it’s not the intended use.

Expandabilitysierra designs flex hike day pack

The biggest feature of this pack is adjustable volume. This feature is invaluable; it adds so much versatility to the pack, and I never have to worry about cramming everything I need in a day pack again. Changing this throughout your hike is easy to do, and I had no struggles when adjusting the volume. The pack carries well with almost nothing in it, as well as when it’s completely stuffed (which I definitely managed to do).

Fit & Comfort

The Flex Hike Day Pack is adjustable to basically any torso size. Adjusting the length was also quick and easy. The straps and hip belt are built rugged enough to handle a good amount of weight but are also slim enough that they don’t feel cumbersome when carrying a light load. My one complaint about the fit is the padding in the lumbar area protrudes a bit and is rather firm. It would dig in uncomfortably sometimes, particularly if I had a full pack. However, this discomfort usually disappeared as I wore the pack and wouldn’t be noticeable a short distance into the hike.


I dragged this pack up mountains, took it out in the rain, took it through airport security, and stuffed it under an airplane seat. Despite that, the materials have held up well, and I have no question about the durability of the fabric or the mesh. One small issue I did notice was that one side of the hip belt buckle broke while I had it in storage. I’m not exactly sure how; someone might have stepped on it. However, it still functions fine and isn’t uncomfortable. I’m sure it would be an easy repair if I wanted to fix it. The pack does also come with a limited lifetime warranty.


  • Versatile for many trip types with easily adjustable expanding volume gusset
  • Lots of pockets for snacks, wallets, and whatever your heart desires!
  • Adjustable torso and hip belt sizing for a one size fits all and easy sharing between friends
  • Durable fabrics: the mesh is particularly strong and holds snacks and water bottles well with no signs of wear


  • The lumbar padding can be uncomfortable if it’s packed full; I found this to go away over time.
  • The plastic hip belt buckle broke but still functions as intended.

Final Thoughts

The Flex Hike 20-30 Pack is truly a one-of-a-kind day pack that has a ton of versatility. I’d highly recommend it for those who go on a wide variety of adventures or just want a solid day pack that can hold up to wear and tear. The pack is reasonably priced and lightweight compared to other day packs out there.  It’s even more reasonable when you consider all the features it includes. This pack is my first choice when looking for a day pack, and I’d bet it would make your shortlist too.

Shop the Sierra Designs Flex Hike Day Pack

Comparable Packs

Patagonia Refugio Daypack 30L

Weight: 1 lb 12 oz

MSRP: $129

REI Co-Op Trail 25 Pack

Weight:1 lb 15 oz

MSRP: $79.95

The Sierra Designs Flex Hike Day Pack was donated for purpose of review.

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