Many backpacks are specialized to meet the specific needs of the users. One such specialty backpack is the one equipped with hydration packs. These are designed to provide for water supply when the user is on the more or busy hiking.
The secret to a good backpack is the fit and the capacity to hold the load. Usually the fit would really depend on the body type of the user so bigger may not necessarily be right or smaller is perfect. It would also depend on the purpose of the backpack.
Purpose – consider the style that you want to use and where you are going to use it. There are internal frames and external frame backpacks. The internal frames are the favorites of backpackers who go on extended trips. However they are also more expensive than the external frames.
Daypacks vs. backpacks – these are actually the smaller cousins of the backpack. These are great for day treks and for school use. They may be smaller but they can hold laptops and are lightweight. They can also cost cheaper.
Hydration system – there are specialized backpacks which are designed to offer a constant supply of water even when on the move. The bladder of the system is made of quality plastic which can hold the water. The water is accessible thanks to the drinking hose that usually goes with it, although there are some models where the hose is sold separately.
Durability – choose the double stitched seams, not single stitched. The materials used should also be waterproof rather than water resistant. One clue to help differentiate between the two is the availability of colors. As waterproof materials are most likely to be nylon/polyester blends which is available in thousands of colors.
Straps – these should be wide and padded. The padding may be made from a variety of materials but it is best to avoid those made from foam as they could pucker up, develop hot spots and then just disintegrate. The wide straps are a better choice for there are less chances of cutting into the skin.
Fitting – before buying, make sure to fit the backpack first. If it is too long for the torso then it can sag to the back, if it were too short for the torso then there would be no support for the lower back which could cause pain and soreness.
Light weight materials – there are some materials which are very durable but are very heavy. Add the weight of the bag plus the contents could be uncomfortable for the user. The light weight materials are just as durable as the heavy weight ones and they are also waterproof, not water resistant.