Expandable backpacks are such underrated bags yet, they provide unrivaled versatility compared to regular backpacks. Take for instance, an expandable backpack such as the Osprey Transporter Roll. It has a nifty rolltop mechanism that lets you roll it up to fit a lot of stuff, as well as roll it down with a bit of stuff so, you aren't carrying a bulky bag!
The Osprey Transporter Roll has a hip belt built-in, which consists of two thin webbing straps attached to a buckle clip. The hip belt straps measure 46cm long and integrate ladderlocks to regulate the length of the webbing. Backpacks with a hip belt system are ideal because they help to stabilize the backpack, as well as transfer the backpack's weight from the shoulders to the hips.
A hip belt can transfer as much as 80% of the weight, provided that the hip belt is properly padded and has a good length to it to wrap around the hips. The Transporter Roll's hip belt is long enough to stabilize the bag on the hips but, it isn't padded; hence not as much weight gets transferred from the shoulders to the hips.
The Osprey Transporter Roll shoulder straps measure 42cm long and have a curved, beveled design so, they are wider at the top (7cm) and narrower towards the bottom (5cm). The shoulder straps have a wide spacing to accommodate broad shoulders and, they are joined at the top via a seamless piece of fabric, which prevents the shoulder straps from wiggling and rubbing against the sides of the neck. Just above the shoulder straps, there is a thickly padded grab handle, measuring 20cm long, 2cm wide and 0.5cm thick. The grab handle is internally sewn for reinforcement.
The Osprey Transporter Roll shoulder straps are thinly padded (6mm thick) but they're made with closed-cell foam, which is springy. The backside of the shoulder straps are covered with breathable fabric mesh, while the front of the shoulder straps feature two small pass-through straps, as well a sternum strap system to keep the shoulder straps closer together. The sternum strap is attached to a ladderlock with a 30cm long webbing strap to regulate the length. The sternum strap features a slider at either side so, you can can adjust the chest strap up the collarbone and down towards the breastbone area.
The Osprey Transporter Roll rests comfortably on the back without generating too much heat, thanks to the v-shaped foam padding and the same orthopedic foam design found on the Arcane daypack and Arcane duffel version. The v-shaped padding on the Transporter Roll measures 42cm long, 9cm wide (at the top) and 19cm wide (at the base). 
The ridged design of the foam padding makes it very comfortable on the back and also minimizes the build up of sweat even better than the previously mentioned Arcane packs. That said, the Arcane duffel version has a nifty should strap system that lets you hide them inside a pocket so, you can use the bag like a briefcase.
The Osprey Transporter Roll outer shell is entirely made of 400D nylon material, which is double coated with TPU, giving the Transporter Roll a thick rubbery finish. Being made of TPU, the Transporter Roll is incredibly hydrophobic so, water beads and rolls off the bag. The double coating layer of TPU on the front also extends to the sides and base of the bag, which have army green accents and are made of slightly thinner denier nylon (360D). 
Being properly reinforced, the Transporter Roll doesn't have issues of water ingress from the bottom of backpack. It's thoughtful also that TPU material has been used to waterproof the Transporter Roll because it is scratch resistant too. Bags that are waterproofed with PU material aren't so, they are easier to scratch than even a non-coated polyester or nylon backpack. Branding on the Transporter Roll has been kept minimal with just a subtle Osprey logo heat printed on the front of the bag.
Being a rolltop, the Osprey Transporter Roll has a top loading opening that can be extended up to 18 cm high to increase the capacity to a maximum volume of 25 litres. The rolltop opening does not have a zip so, you have to fasten it by folding the rim 2 inches down. When fully extended, the total height of the Transporter Roll is 60cm high. The rolltop can be compressed down to 44cm, which is perfect to prevent small loads from shifting around. 
The camouflage pattern is found on the front of the bag where there is also a long webbing strap for fastening down the rolltop. The rolltop webbing strap measures 70cm long and 3.5cm wide and, it's stitched up to the front base of the bag. There is small pass-through strap on the front of the bag designed to route rolltop strap and keep it upright. 
The small pass-through strap is attached to two small plastic retainers, which are sewn on to the fabric of the bag. The pass-through strap measures 6cm long and, it's also useful for clipping other things on to the bag. The rolltop strap integrates a large, quick release metal G hook that measures 5.5cm long and 4.4cm wide. The buckles and ladderlocks are made of plastic and are YKK branded.
The Osprey Transporter Roll has no internal lining, which exposes the raw nylon material. The lack of lining isn't actually a problem since the bag has a double coating of TPU on the outside and the off-white nylon color actually works since it illuminates the inside of the bag. It's actually nice that the nylon has not been dyed internally since rarely, these days, you get to see the natural color of nylon.
Inside the Osprey Transporter Roll, there is a built-in storage insert that has a similar footprint to a car back seat organizer, featuring a couple of elastic mesh pockets and two well-padded sleeve compartments for a tablet and a 15-inch laptop. The internal storage insert measures 43cm long and has been positioned halfway the length of the bag and 7.5cm above the the base to prevent bottom impacts. The base of the storage insert has also been thickly padded, which is great. The sides of the tablet/laptop sleeves have some padding, although the're not as thick. 
The smaller sleeve measures 32cm long and 25cm wide, while the larger laptop sleeve measures 40cm high and 29cm wide. The mesh pockets measure 12cm long and 8cm wide so, they're large enough to keep a small water bottle. There is also a built-in plastic keychain attached to a thin red webbing strap, as well as two small holders for smaller items like a pen, flash USB drive, energy bar, etc. The minimal, slimline design of the internal storage insert allows the Transporter Roll to have a really spacious single compartment.
The Osprey Transporter Roll also has hidden zippered side pockets, which are narrow and measure 10cm deep and 30cm high. The side pockets have regular zips with a finger loop cord pull tab. There is no TPU coating on the seams to prevent water ingress but, the side pockets are located under the outer TPU shell, which acts like a canopy over the zip compartments. You can buy the Transporter Roll from Osprey and amazon. Check out the review of the Arcane XL Day backpack and  Osprey Talon Earth 22 Limited Edition techncal daypack