"Lehar V. Osvald" wrote in message
om...
I don't know anything about backpacks, unfortunately. I've always used
cheap ones and I have one problem with them--my back sweats heavily
and this gets the pack dirty after a while. I have started shopping
and I see that there are packs with two long aluminum things attached
beneath the shoulder straps. I assume this is what is called an
"external frame" backpack.

The long aluminum things you describe are called 'stays'. The are used in
larger internal packs to provide support and enhance the suspension of the
pack. An external frame pack has a tubular rack on the outside of the pack.
..