Knack NAT Convertible Duffel Review: A 24 to 40 Liter Travel Chameleon

Introduction

The Knack NAT Convertible Duffel is a large panel-style opening travel pack that shares the sleek design language of Knack’s Series 2 packs. Updated in 2020 to include a larger front organizational compartment, side handles, and locking zippers, this convertible duffel focuses on something different: a simple, large internal compartment rather than easy-access external organization. If you like packing with cubes and want a bag that can shrink for a weekend or grow for a longer trip, this design deserves a close look.

Size and Carry-On Flexibility

In unexpanded mode, the duffel works as a day pack or a smaller weekend travel bag. The listed length and width dimensions are fairly accurate at about 19 by 13 inches, or 48 by 33 centimeters. The listed five-inch depth is a little ambitious, though: packed the way most people actually pack it, it measures closer to six to seven inches.

That depth means the bag works as a carry-on on pretty much every airline, and although the length runs slightly over, it easily fits into a personal item sizer box, so you can also use it as a personal item on many budget airlines.

A zipper runs around the full length of the pack and opens it into expansion mode, adding a few extra inches of depth. Capacity jumps from 24 liters unexpanded to 40 liters expanded, and the depth grows to roughly nine or ten inches depending on how full you pack it. It still works as a carry-on expanded, but fitting it under the seat as a personal item becomes a lot harder.

Materials and Hardware

The duffel uses some of the best fabrics and hardware in the Knack lineup. The shell is a medium-thickness but very durable 420 denier high-density nylon, noticeably smoother than the thickly woven nylon used on many travel backpacks. Hardware quality is strong throughout: YKK zippers with custom zipper pulls, large nylon Duraflex buckles and adjusters, a metal buckle on the shoulder strap attachments, and a clip on the sternum strap.

The main compartment zippers are locking, while the laptop compartment zippers are not. The main compartment uses smaller number-eight zippers rather than the beefier number-ten style seen on some rivals. Number-tens are big and durable but slower; the number-eights here are smaller yet much smoother, which suits this pack well.

External Features: Bottle Pocket and Laptop Compartment

The exterior mostly focuses on the carry system, with almost all small-gear organization living inside the main compartment. The front of the bag has nothing at all: no pockets, no compartments. There are two side carry handles, a luggage pass-through sleeve, and a secret pocket on the back.

The side water bottle pocket looks unassuming from the outside because its zipper sits almost flush with the bag, so all of its volume sits inside rather than bulging outward. It runs all the way to the bottom of the pack and easily holds a standard slim bottle or a full one-liter bottle. The pocket is fatter at the bottom and tapers upward, making it a good home for long, skinny items like a travel tripod, with a max depth of about 14 inches. One caution: anything you put in here takes up volume from the main compartment.

The laptop compartment opens via a side-access zipper located behind the back padding. It easily holds a 15-inch laptop, with thick, squishy memory foam padding on top, a thin piece of padding between the laptop and the main compartment, and memory foam at the bottom, though there is no false bottom.

The Carry System

The shoulder straps are decently wide with medium padding and a squishy, soft mesh back. The foam here is the lighter-weight closed-cell style with larger air bubbles: softer and squishier, but it compresses more under heavy loads. That contrasts with the denser EVA-style foam found on some competing travel packs, which feels stiffer on the shoulders but holds up better under serious weight.

Because this is a convertible duffel, the straps are stowable. Unclip the small lobster claw buckles at the bottom and tuck the shoulder straps into the top zippered pocket.

Back padding is very soft and comfortable, made from a squishy EVA memory foam with decent air ventilation channels. Behind it sits the luggage pass-through sleeve so you can stack the bag on rolling luggage. The advertised secret pocket is genuinely hidden: the zipper is sewn in behind a fabric flap inside the pass-through sleeve, making it almost impossible to see unless you know it is there. It is just about deep enough for a passport and a travel wallet.

With the straps stowed, you can carry the bag like a briefcase, or attach the included wide-padded shoulder strap using the two corner buckles and carry it over your shoulder. That duffel-style carry works great in the 24-liter mode.

Interior Organization and Packing

The bag opens with a full zip panel into one large main interior compartment. Remember, the design prioritizes internal capacity over quick external access: other than the water bottle pocket and the secret pocket, all organization is inside.

A compression flap squishes your gear down and includes a large mesh pocket. The lid adds two pockets and a fuzzy-lined sleeve: a larger mesh pocket in the middle and a smaller fuzzy-lined fabric pocket on top, plus stretchy bungee attachments for small, frequently needed items.

Packing cubes work really well in here because the interior is 13 inches wide. Two large NAT cubes fit pretty much perfectly in the bottom of the pack uncompressed, with a little room left over to compress them or squeeze in extra items. The larger Peak Design cube also fits well, though it is big enough that you would likely use just the one, leaving room on top for a toiletry kit, a rain jacket, and a small gear pouch.

The flap and lid pockets handle the rest: items you do not need readily go in the flap pocket, while smaller electronics, pens, and things you want easy access to go in the lid pocket. You can reach the top pocket without fully opening the bag, but the pockets lower down the zipper line really require opening the lid completely.

Fully packed out with gear (no water bottle or laptop), the bag weighed about 5.5 kilograms, or 12.1 pounds. On the back it sits as kind of a rectangle, but the padding is soft and comfortable, and the strap design works well in the unexpanded 24-liter mode. Expanded to 40 liters and loaded with a laptop and water bottle, though, carrying it all day can get heavy.

Should You Buy It?

The NAT Convertible Duffel is a good choice if you want a well-made pack with large volume for its size. Unexpanded, it is small enough to work as a personal item on many airlines as long as you do not overpack it, making it a great getaway bag for shorter trips. Expanded, it stretches to 40 liters for longer trips.

The main downside is the lack of external organization: outside of the water bottle pocket and the secret pocket, there are no pockets or compartments for smaller gear. Knack does offer decent organization inside the pack, some of it reachable from the outside, and this duffel style pairs naturally with gear pouches. If that trade-off suits how you pack, this bag is easy to recommend.

Conclusion

The Knack NAT Convertible Duffel delivers premium materials, smart convertible carrying options, and a genuinely useful 24-to-40-liter range in a package that still fits airline size limits. It asks you to embrace inside-the-bag organization, and for cube-based packers, that is a fair trade for the clean exterior and generous internal space.