Gear Review: Sea to Summit Flow 35L Dry Pack

Sea to Summit Flow 35L Dry Pack
Sea to Summit Flow 35L Dry Pack

Waterproof Backpack
Sea to Summit Flow 35L Dry Pack
$200, 35L/2,136 c.i., 2 lbs. 4 oz.
One size

We reached the first, deep pool of water that we had to swim across in the narrow canyon called The Subway, in the backcountry of Utah’s Zion National Park. I tucked my expensive camera gear inside my new Sea to Summit Flow 35L Dry Pack, with my food and extra clothing—and hoped this pack would prove true to the company’s claim of being infallibly watertight. (I did put my camera gear inside another dry bag first, of course.) Then I dropped into the frigid pool—wearing a dry suit—and kicked across it, floating the Flow. And yes, it did keep its contents completely dry—thankfully. But more than just a glorified dry bag with shoulder straps, it proved itself to be a solid and comfortable pack for hiking all day, too.

I carried the Flow 35L with 15 to 20 pounds inside—including, at times, a full dry suit in a stuff sack—on a one-day hike and descent of the Subway in Zion, which took us just under seven hours car to car and involved three swims across pools, a lot of walking in water, and about six miles of hiking the trail above and below the Subway. The perforated foam shoulder straps and hipbelt were comfortable with that much weight, and drain water and ventilate well, and the hipbelt is removable to shed a few ounces of weight.

Flow 35L Dry Pack harness.
Flow 35L Dry Pack harness.

A top-loader with a roll-top closure for the main compartment, the Flow 35L is made with TPU-laminated, 420-denier nylon and is fully seam sealed. Water never penetrated the pack’s main compartment when I floated it across deep pools. You have to nearly fill the pack to create enough tension on the roll-top closure to ensure a watertight seal, but side compression straps help make a slightly undersize load watertight.

This pack is bulletproof—I slammed it into canyon walls and dropped it repeatedly onto rough sandstone, and it’s no worse for the wear. But the stretch mesh side pockets, big enough for a liter bottle, are its only vulnerable part. The upper compression strap on each side has two positions of attachment, to accommodate attaching objects of different sizes; I fit a fairly large tripod under the straps.

I didn’t quite fill the Flow 35L for the Subway, but 35 liters is a good size for technical canyon descents of a full day or even two days if you pack light, when you may be carrying a longer rope and more gear than we needed for the Subway. A white interior makes it easier to see contents. I like the big, top handle for lifting and lowering the pack through tight spaces even while wearing neoprene gloves.

Sea to Summit Flow 35L Dry Pack.
Sea to Summit Flow 35L Dry Pack.

Organization is basic, as expected in a dry pack (to minimize potential points of leakage). There’s a zippered, internal, stretch pocket for small items like keys and phone. A two-liter front pocket has a waterproof zipper with a rain hood; it keeps out rain and water if briefly immersed, but is not completely waterproof in a sustained immersion. There’s also an externally accessed, zippered pocket for a water bladder, so you can refill it without having to open the main compartment and potentially exposing its contents to water.

Sea to Summit Flow 35L Dry Pack.
Sea to Summit Flow 35L Dry Pack.

For canyon hikes when you’re in water, river trips when you want a dry pack that offers real support for 15+ pounds for side hikes, or any hikes in consistently wet environments, the Flow 35L Dry Pack is a durable choice.


You can support my work on this blog, at no cost to you, by clicking any of these affiliate links to purchase this at, or the similar Sea to Summit Hydraulic 35-120L Dry Pack at or, or any of Sea to Summit’s dry packs at

NOTE: I’ve been testing gear for Backpacker Magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See all of my reviews by clicking on the Gear Reviews category at left or in the main menu.

—Michael Lanza


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Leave a Comment

11 thoughts on “Gear Review: Sea to Summit Flow 35L Dry Pack”

  1. Great review! I’d be interested to hear your thoughts on the maximum load you would consider carrying with this backpack. Thanks.

    • Thanks, Haj. As the review indicates, I didn’t put in enough weight to see where the pack maxes out for comfort and Sea to Summit does not provide a weight capacity. But based on the internal frame and harness setup, I think it’ll be comfortable with 25 to 30 pounds and maybe more for some people.

  2. Hi Michael
    I have a black sea to summit flow 35L for about a year now, I was very happy with it until yesterday – and reading your review! On February 5th 2019 I was up Bowfell in the English lake district and my backpack has not been submerged in water at all , the rain stated at around 1.30 pm coming down from the summit and I reached my car by 4.30 pm, in this 3 hours time frame – the contents inside the 2 Litre front pocket had become soaked with lots of expensive equipment in there, I was not happy at all especially as this pocket area has waterproof written/stamped on it , 3 hours of rain is not much at all especially as I paid quite a lot for the backpack here in the UK!

    • Hi Mark,

      I’m sorry to hear about your damaged equipment, that’s disappointing. Personally, when I know a pack could get wet, even an ostensibly waterproof pack, I like to double-protect important contents by using waterproof stuff sacks, too.

      I contacted Sea to Summit about your comment and provided this response:

      “First of all, we’re sorry to learn that you had a less-than-positive experience with your Flow 35 Drypack. We can imagine how frustrating that would be.

      “As Michael notes in his review of the pack, the ‘main compartment (of) the Flow 35L is made with TPU-laminated, 420-denier nylon and is fully seam sealed,’ and he observes that, ‘Water never penetrated the pack’s main compartment when I floated it across deep pools.’

      “However, he also notes that the ‘two-liter front pocket has a waterproof zipper with a rain hood; it keeps out rain and water if briefly immersed, but is not completely waterproof in a sustained immersion.’

      “The reason for the difference in performance between the main compartment and the external pocket and the main compartment is that the pocket is sewn flat on to the body of the pack and therefore the seam cannot be taped. For this reason, the hang tags supplied with the Flow at time of purchase contain an advisory that the front pocket will keep contents dry in a light rain and splashes but is not completely waterproof.

      “However – none of the above should be taken to mean we don’t take your issue seriously. Several of us here in the Boulder, Colorado office have experience of the Lake District and know just how wet it can be. If you would like more details on the Flow DryPack, please email us at [email protected] and put ‘Flow 35L Pack – external pocket water entry’ in the subject line.

      “Again, our apologies for the inconvenience.

      “The Sea to Summit Team”

  3. Hey Michael, thanks for the great review! I know this is an old post, but I’ve been eyeballing this pack and yours is one of the few reviews on it. Do you have any experience using this as a carry-on bag for flights? I saw an estimate of the dimensions that are just over the maximums but was curious if you had any experience.


    • Hi Dan, good question. I have not used it as a carry-on, but I’ve certainly used packs in the 30-35L size range as carry-ons without a problem. The Flow 35L isn’t rigid, and while I can’t say for certain, I think you’d be able to use it as a carry-on and fit it in the overhead bins on most commercial flights.

      • Hey Michael,

        Thanks for the quick reply! That’s what I suspected. I’ve seen some rigid carry-ons that have no business in an overhead…

        One other follow up: It sounds like you’ve used it a fair amount hiking. I’m not sure how much if at all the design has changed but the back padding doesn’t appear to be designed with much air flow in mind. How was the back ventilation? Did it seem to just get hot and swampy on your back or ventilate ok? I know it won’t be the same as a suspended mesh frame but I tend to hike pretty hot.

      • Hi Michael,

        Thank you for the quick reply! That’s about what I thought as well. Hopefully we’re both right! I had a quick follow up question as well: How well does the back support foam ventilate? I’ve had some packs where once you start moving it is miserably hot and swampy on your back. I know this isn’t a suspended mesh design but with your hiking experience is it comfortable? I tend to hike hot and the solid looking back panel makes me a bit nervous.

        P.S., sorry if this is a double post, thought I commented before but don’t see it up.

        • Hi Dan, you raise a good question. As you can probably see from the photo of the back panel, it’s not really designed for air flow; it’s designed for closely hug the torso. Considering that this pack is intended for use in water–often cold water, when the challenge is staying warm rather than staying cool–that design makes sense because it also helps the pack carry more stably and comfortably.

    • Thanks Jon. I didn’t test this pack with the amount of weight I’d carry in a climbing pack–25 to 35 pounds–and I’m not sure how comfortably it would handle that much weight. While it has the durability of a climbing pack, it does not have the features I’d normally look for in a climbing pack, like external tool attachments, a rope strap under the lid, and durable external loops for lowering the pack. For $200, you can find a pack that’s designed for climbing.