Backpacks are usually obtainable in three categories: External Frame; Internal Frame; and Daypacks.
External Frame - typically constructed employing a ladder-like frame of aluminum or plastic using a separate pack bag attached usually utilizing clevis pins and split rings. The hip belt and shoulder straps are affixed to the frames. Volume capacity of the backpack varies from 3,000-4,500 cubic inches (49-73 L). The external frame backpack allows space for attaching large items (e.g. sleeping-bags) out of the frame making the carrying capacity more than the volume of the backpack. Features to watch out for in a backpack include: good lumbar padding, a conical hip belt, recurved shoulders with higher padding, as well as a chest compression strap.
*Weight carrying capacity
*More air space so back doesn't sweat as heavily
*Weight carried higher in backpack allowing more upright posture
*More outside pack capacity allowing for versatility in packing
*Generally more affordable when compared with internal frame backpack
*Raises center of gravity making hiker top heavy and much less stable
*Doesn't hug body and risks wobbling laterally
*Can cause problems with balance when skiing or snowshoeing
*Must be boxed around prevent damage when traveling by plane
Internal Frame - uses materials like aluminum stays, carbon fiber, plastic sheets, and foam to make a rigid spine this agreement the hip belt and connectors are attached. The backpack extends the total height with the pack with compartmental divisions. Pack volume varies from 3,000-7,500 cubic inches (49-122 L). Internal frame backpacks needs to have the same comfort features because external frame described above. Also choose a fabric layer sewn around the top opening from the pack bag allowing the most notable pocket to be lifted up providing space for additional storage of equipment and side compressions straps that squeeze the pack down when carrying an inferior load.
*Carries plenty of weight
*Conforms to body for better balance
*More comfortable to wear for extended periods
*Back perspiration more common
*More fixed carrying capacity
*Bending over more from lower center of gravity
*May be more expensive
Daypacks - no frame, runs on the foam or plastic sheet for back panel. To hold heavier weights search for these features:
*Well-padded shoulder straps
*Foam hip belt in contrast to just a webbing strap
*Chest compression strap
*Volume capacity up to 3,000 cubic inches (49 L)