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February 2023 Issue
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Sierra designs Flex Capacitor 25–40l

Lightweight, versatile tramping pack with expansion capacity.



Our Rating:

Lightweight, versatile tramping pack with expansion capacity.

Plusses: Expandable capacity, supportive and comfortable frame, seven pockets
Minuses: Zip flap could be improved

Weight 1100g

Features: The distinctive-looking and cleverly named Flex Capacitor fits a bunch of features into a well-designed thru-hiking style pack. Primarily, it has a gusseted main sack that can be expanded with four straps. A strong Y-shaped alloy tubing frame supports a simple but durable harness and the hip belt has two large pockets. There’s food, water or accessory pockets on the shoulder straps, a lid pocket and small stretch water bottle pockets on the sides. Inside is a removable mesh hydration sleeve and the whole pack is closed with a chunky #10 YKK zip. Two ice axe loops could also hold hiking poles. 

Fit: There are two sizes: S-M and M-L, but otherwise this is a unisex pack. I’m 1.76m and the S-M fitted me really well. It’s relatively narrow, so probably will best suit slimmer people. 

In use: The one large compartment is easy to pack. There’s a choice of packing it with the compression straps limiting capacity or using the straps to compress the load after packing it to squish down softer gear and keep everything stable. I liked this versatility. Furthermore, the abundant compression straps make carrying overflow gear like camera tripods or hiking poles easy. The removable mesh hydration sleeve can be toggled to the pack’s exterior for carrying water or wet gear. My only complaint from using the pack was that the main zip sometimes caught on the zip flap. I also thought this otherwise excellent pack would be better served with a roll top closure, as that would be a better match with its design as well as being more water resistant. This pack reminded me of the excellent Exped Lightning 60, which I used for Te Araroa, but I prefer the Flex Capacitor’s narrower shape and sturdier compression. 

Comfort: The harness is designed to be durable and failsafe. Thick lumbar and shoulder padding push the load away from your back while still providing cushioning and support. It’s not as ventilated as packs with breathable mesh, but I think this will make it last longer. Overall I found the pack to be great for loads catering for a few days – which is really what this capacity is designed for. In particular, the hip belt is very supportive being built to cope with heavier loads, while the frame is designed to pivot between shoulder straps and hip belt.

Value: For a relatively simple, non-adjustable back length design this pack is not particularly cheap, but it’s also more of a specialist than an all round tramping pack.

Verdict: This is an adaptable, lightweight pack ideal for people thru-hiking or doing unencumbered long weekend tramping trips.