This is an excellent pack, especially for heavy loads. It’s designed to allow good freedom of movement whilst still being very stable and it achieves both aims. The hipbelt attaches via a ball-joint so it swivels as you move whilst still supporting the load. The amount of movement can be controlled with side straps from the pack to the belt. An Allen key is provided for adjusting the ball joint. The shoulder straps also have some give and their length adjusts as you move. This flexible harness makes the Boost a good pack for scrambling, climbing and skiing. The back and harness are covered with soft mesh that may slightly reduce sweat build-up but there is little ventilation so a sweaty back is likely. The Boost handles 6kg without problem and should be fine with much more.
The Boost comes in two sizes. There’s also a women’s specific version called the Flare, again in two sizes.
The pack has good pockets with a large stretch pouch on the front, a roomy lid pocket and stretch side pockets easily big enough for water bottles – I can get the latter out but not back in when wearing the pack. Black Diamond’s litres are on the large size as the pack is as roomy as 35 litre ones.
The drawbacks of the Boost are the high cost and weight. Against that it has a unique and effective back system and functional easy-to-use features.