My buddy Stuart Palley and I went fishing on the Sea of Cortez a few days ago. We knew we’d be in an open panga, with plenty of salt water coming into the boat. And in that environment a professional photographer would normally carry his bodies and lenses in a hard-sided Pelican case. But Stu wanted to travel with just a carry on when he flew down to see us here in Todos Santos. So, we just balled his expensive equipment up in a few clothing layers for padding, and threw it in this Filson backpack.

　　Made from thermoplastic-coated 840 Denier nylon canvas, with seams welded by radio frequency (RF), a technology that uses high-frequency radio waves to melt layers together (a novel kind of bond that requires no adhesive or stitching), and closed by a completely waterproof TIZIP zipper, this backpack is made nearly identically to the heavy duty dry bags you and I have taken boating for the last few decades. What’s new here is that, all of a sudden, those materials and technologies are popping up on backpacks designed for everyday use, in activities both exciting and mundane.

　　“TPU-coated nylon is made by bonding a nylon base fabric between thermoplastic polyurethane (a specific type of heat activated plastic), creating a multi-layer fabric sandwich that is an incredibly durable, flexible, waterproof performance material,” explains Alex Carleton, Filson’s Chief Creative Officer. “The material has been around a while, but advancements in fabric and the RF welding technologies have made it more accessible to a wider number of brands.”

　　I started shopping for durable, practical waterproof backpacks while preparing for a peninsula brown bear hunt with my wife off the coast of Alaska last year. And while I was expecting to find the familiar roll-top dry bags, just fitted with backpack straps, I think I stumbled onto an emerging trend in the backpack space. Both of us found ourselves spoiled for choice with a wide variety of packs available in different sizes, and a selection of features from brands both familiar and new.

　　And not only did my Filson bag survive 14 days hopping in and out of skiffs around the rocky shores of Alaska’s sea islands, but I’ve since found it perfectly suited to a variety of other trips too.

　　I didn’t really need a waterproof bag to fly to France last October to nurse my mom through a major surgery, but it was still the perfect size for a carry-on, and its slick material made it easy to slide in and out of the planes, trains, and rental cars it takes to get to my parents’ remote farm. And I appreciated the entirely air-tight construction when I stopped in Paris on the way home, for a good meal, a nice bottle of wine, and a much-needed mental health break in a comfortable hotel. But I’m sure you’ve seen the headlines—Paris is besieged by bedbugs. So I hung the waterproof backpack from the shower head in my hotel’s bathroom, and made sure the waterproof zipper was pulled entirely closed. I can’t confirm if it was the backpack or not, but I can tell you I brought zero of the hard-to-kill pests home to Montana.

　　I also grabbed the same bag to transport my laptop, toiletries, and travel clothes for a two-week long drive down to Todos Santos, where my wife and I are currently spending two months while recuperating from another major surgery. While my truck bed is capped with a GoFastCamper, all the gaps and holes Ford left back there to drain water also create a lot of dust ingress. An airtight bag is just as good as keeping dust out as it is water. I roughly shoved the backpack into whatever small void was available inside the camper before each day’s drive and I didn’t have to worry about where it got hurled while unpacking for camp each night.

　　“This material is a great balance of weight, flexibility, durability, and cost, while not compromising on submersible waterproof performance,” continues Carleton. “A double-sided TPU-coated dry bag is perfect for users that expect submersible performance without the bulk and weight of a hard-sided case. Waterfowl hunters, fly fishers, kayakers and boaters, motorcyclists… any user who is out on the water or under threat of serious weather could benefit from a welded TPU-coated dry bag. Whether a full waterproof backpack, or using a smaller waterproof roll-top gear bag as a dry packing cube within a separate non-waterproof bag, they have peace of mind that their important gear is safe from the wet.”

　　Carleton goes onto explain that TPU is very different from other materials used to create cheaper products.

　　“Our TPU-coated fabrics are waterproof, durable, abrasion-resistant, tear-resistant, and puncture-resistant, and more environmentally friendly than alternatives, as they do not release toxins when heated, do not contain phthalates, and are recyclable,” he states. “They also maintain their flexibility in lower temperature environments, like snow and cold water.”

　　“TPU coated fabric should not be confused, however, with inexpensive, more toxic vinyl alternatives like PVC (polyvinyl chloride) or EVA (ethylene-vinyl acetate), which you see flooding sporting goods store shelves through inexpensive soft-sided coolers and dry bags,” Carleton continues. “Although they have a similar look, these vinyl materials are inferior and less environmentally friendly to produce. They are inexpensive to make, but can release toxic fumes when welded, and often have additional plasticizers, phthalates, and other potentially harmful chemicals. These inexpensive alternatives are not as durable, are less abrasion-, tear-, and puncture-resistant, and tend to become brittle at low temperatures.”

　　Let’s take a look at some of the best applications of TPU-coated nylon currently available in backpacks that are practical for everyday use.

　　The Best Dry Bag Backpack: Filson Backpack Dry Bag ($365) With a 28-liter capacity, Filson’s zip-closure backpack is a little on the small side for extended travel, but perfect if you’re squeezing in and out of cars, and boats, or just walking through a city or the woods. While the water bottle sleeve is way too small to actually hold a water bottle, the welded carabiner attachment points, shell holders, top strap, and other connection points mean you can easily connect to the bag in multiple locations. The built-in side accessory pouch and clear plastic rear panel aren’t submersible, but I find them perfect for stashing weather-resistant necessities like my Garmin inReach, headlamp, ear plugs, and stuff like that.

　　The main compartment is entirely open, with only a small mesh panel available for organization. So you may want to add a laptop sleeve or similar. I’ve been using mine almost every day since last May, and it still looks brand new.

　　The Most User Friendly Dry Bag Backpack: Osprey Arcane Roll Top Waterproof 25 ($270) My wife has limited mobility in her left hand, so she finds roll-top closures and hard-to-pull waterproof zippers difficult to use. She was worried she might make too much noise fussing with one of those, and risk spoiling our hunt, so it was a relief to find the Arcane. While you need to roll its top at least three times to assure it’s actually submersible, that flap also contains magnets that can silently connect it to the body. And we found that was plenty to keep spray and precipitation out, even while riding in a small skiff in heavy seas.

　　This would be the bag I’d choose if I still commuted to an office by bicycle, instead of to my couch in my underwear.

　　The Best Dry Bag Hip Pack: Mystery Ranch High Water Hip Pack ($169) Toothed zippers like the TIZIP used on the Filson pack and shared with dry suits are difficult to pull and are so strong they’ll destroy any other fabrics you catch in them. To avoid those problems, Bozeman-based Mystery Ranch employs the toothless Tru Zip system, which uses an extruded TPU slide instead.

　　Made from a similar 840 Denier nylon base fabric to the Filson, this five-liter hip pack is perfect for keeping smaller items safe from submersion or weather.

　　The Most Comfortable Dry Bag Backpack: Orvis Pro Waterproof Backpack 30 ($329) Slightly larger at 30 liters in capacity, and made from similar materials, this Orvis pack features a sleeker shape than the Filson, and includes rod holder cam straps on its right side as well as a functional water bottle sleeve on the left. More importantly, its padded back panel and shoulder straps are more breathable. So if you plan to put in miles while carrying a dry bag pack in hot weather, this may prove the superior choice.

　　When Are Dry Bag Backpacks The Wrong Choice? Jake Stern, Outside’s digital editor found this out the hard way while ski touring earlier this year. His coffee mug spilled inside a waterproof pack, and with nowhere to go, that warm, sticky liquid just hung around, soaking all his layers.

　　“For users who want water resistance, but don’t need submersible performance—like hikers or commuters in the rain—a welded TPU-coated dry bag may be overkill in performance and cost,” acknowledges Carleton. “These users would benefit more from a sewn weather resistant bag made of waterproof fabrics.”