Sierra Designs Flex Summit Sack

The Sierra Designs Flex Summit Sack is great for many occasions.  This minimalist day pack doesn‘t add weight with unnecessary frills, but keeps useful features that make it a versatile piece of gear.  The Flex Summit Sack is perfect for day hikes, quick outings from camp and even for traveling.  I carried clothes for a three day business trip in this pack and fount it to be great for keeping hands free of luggage.

Sierra Designs Flex Summit Sack
Sierra Designs Flex Summit Sack

The “flex” in the Flex Summit Sack is all about pack volume.  It expands from 18 to 23 liters using three sideways straps on the back of the main body.  If the pack isn‘t full, cinch down the straps to take away extra space and hold your stuff in place.  When hauling food for a family of four, just loosen the straps to make room for the extra.  The three crosswise straps basically act like backpack compression straps and the do the job well.

A U-shaped zipper secures the lid of the Flex Summit Sack to the rest of the pack.  The top opens wide so everything can be put in easily.  There is no other access to the main compartment.  The lid has a small zippered stash pocket on top.  This pocket is big enough for a wall, maps, a first aid kit or other items that you want to keep handy.  A clip to hold a set of keys is there as well.

Sierra Designs Flex Summit Sack
Sierra Designs Flex Summit Sack, big and small

The Flex Summit sack has a hydration sleeve and a port for the hose over the right shoulder strap.  A webbing loop secured with velcro holds the top of your bladder.  If you are like me and prefer to carry water bottles on the shoulder straps, the hydration sleeve can be used for organization.  The Flex Summit Sack doesn‘t add ounces with extra pockets , sleeves, or cubby holes.  I tend to pack in several stuff sacks to organize so I appreciate the clean simplicity a lot.

Stretchy mesh pockets is are on either side of the main pack body.  I tried 1 liter Smartwater bottles and a standard Nalgene bottle in these pockets and they fit just fine.  These pockets are pretty big and will hold a bit more with the water bottles.  These pockets don‘t have cinch cords on top so you have to watch out for anything that will push the bottles up and out of the pockets.  Anything that doesn‘t stick out of the top should ride just fine.

Sierra Designs Flex Summit Sack
Sierra Designs Flex Summit Sack back panel

The Sierra Designs used an airmesh back panel on the Flex Summit Sack.  The pack sits pretty flat on the back so there won‘t be much airflow between the pack and your back but the back panel seemed to help with wicking sweat away.  The shoulder straps are pretty minimal but felt good.  I carried loads of 10 to 15 pounds fairly easily but I wouldn‘t try to load the pack much heavier.  An adjustable waistbelt is provided to hold the pack in place.  The waistbelt doesn‘t carry loads like a hip belt, but it does its job well and you can remove it easily.

The body fabric is 210D Nylon Ripstop which strikes a good balance between lightness and durability.  The test Flex Summit Sack weighed in at 11.55 ounces on my scale and that‘s a tiny bit lighter than the advertised weight.  Sierra Designs says the Flex Summit Sack fits torsos from 16 to 19 inches and waists from 26 to 44 inches.  My torso is a couple inches longer than recommended and I had no issues.

The Sierra Designs Flex Summit sack has an MSRP of $49.95 so it won‘t break the bank.  I think it is a really versatile day pack and I‘ll probably use it to travel quite often.  Day trips with the family will also be an outing for the Flex Summit Sack.  Check out everything Sierra Designs makes at


Thanks to Sierra Designs for sending out a test sample for testing and review.  We have to watch our budget around here just like you do and it is a real privilege to be able to pass along information on products like this.  Hopefully these honest reviews benefit everyone.

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