Whats the difference between the two different capacities listed for some packs, regular and extended?
Most top loading packs close with a drawstring and many large top-loading packs, like internal frame packs, have an extra extension or sleeve of fabric that allows the pack to be overstuffed. When packed normally, like in catalog photos, it produces one volume; when overstuffed it provides another. An example of when you might overstuff a pack is at the beginning of a long trip when you have lots of food. The extra fabric sleeve is often called a “bivy” extension (from the days when mountaineers, caught unexpectedly on day trips and forced to spend the night on the mountain, would empty their packs, put their feet in, and pull their packs as far up as it would go, making a partial sleeping bag or bivouac sack).
