Sierra Designs Flex Capacitor 40-60L Rucksack

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UOG TOP PICK – Flex Capacitor 40-60L Rucksack Since hitting the market back in 2020, the flex capacitor has calved itself out a niche in the outdoor industry, a bag capable of expanding or contracting, depending on how much gear you are carrying this is a fantastic feature. The Flex Capacitor has been a firm favourite of our customers, one of our Top Picks

Sierra Designs says: 

Meet the versatile pack that hauls it all. The Flex Capacitor is a beast of a backpack, constructed from durable nylon for rough conditions in the backwoods or backcountry and built with adjustability in mind. Loosen the expanding horizontal gussets for an additional 15-20L of cargo capacity on longer backpacking trips, or cinch it tight for smaller, compact loads on fast summit days. Plus, ample quick-stash solutions on the straps, sides and bucket lid ensure there are plenty of places to store your midtrail essentials. However you pack it, the Y-Flex suspension adds support so this lightweight backpack can hit well above its weight class.

Our Verdict

Since hitting the market back in 2020, the flex capacitor has carved itself out a niche in the outdoor industry, a bag capable of expanding or contracting, depending on how much gear you are carrying, a truly unique feature that sets it apart from its counterparts; the bag has been a firm favourite here at UOG. The new and improved 2023 flex capacitor is now more user-friendly and more convenient on the trail.

The bag’s main addition is two large elasticated mesh pockets on the front of the bag; these are becoming standard with most rucksacks now, especially in the American market. These large, accommodating pockets are perfect for storing wet weather gear, sit pads, maps etc. The expandable volume of the Flex Capacitor is its unique selling feature, where most expandable packs do so with a longer body; the Flex expands its circumference instead, making it a far more comfortable pack when fully opened. This also provides a far greater range than most of its competitors –the old flex capacitor could expand by 15L, which was truly impressive, whereas the new 2023 iteration can expand by 20L.

The 2023 Flex Capacitor keeps the U-shaped lid access to the pack body, a beautifully simple solution to the heavy lids featured on similar packs. It makes for a rucksack that is refreshingly easy to pack and surprisingly spacious, even when fully cinched down. The Flex Capacitor veritably swallows gear while still providing dedicated space for a hydration bladder and keeping a small zipped essentials pocket in the roof, ideal for navigation kits and snacks. The finishing touches are also present, the hip belt pockets are vast, and each shoulder strap has an additional stretchy pocket which is perfect for storing a water bottle or a mobile phone; it’s brilliant to see these come as standard and not an optional extra.

My only complaint is that the bag doesn’t look quite as striking as the other incarnational, but the 2023 Flex Capacitor 40-60L is the ideal solution to the age-old question of of “what size bag do I need to take?”

– Reviewed by Ultralight Outdoor Gear

Features

• Expandable volume for versatility in use
• Dual adjusting shoulder straps tailor to torso fit
• 2 hyrdation pockets on shoulder straps
• 2 stretch mesh side pockets
• Hydration sleeve doubles as removable summit sack
• Zippered hipbelt pockets
• U-shaped top access zipper
• Lightweight Y-Flex Suspension
• Ultralight weight

Specifications

S/M

• Weight: 1258g
• Volume: 40-60 L (2441 – 3661 cubic in)
• Waist Belt: 28” – 46” (71 – 117cm)
• Torso: 16” – 19” (41 – 48cm)

M/L

• Weight: n/a
• Volume: 40-60 L (2441 – 3661 cubic in)
• Waist Belt: 33” – 50” (84 – 132cm)
• Torso: 18” – 21” (46 – 53cm)

Material & Construction

• 420D Small Back Stafford Poly

Help & advice:

• The Ultimate Guide to Choosing an Ultralight Rucksack
• Time-Saver Guide to Choosing a Rucksack