Lithium - some pics in my album if you want to see what it looks like.
The 45l pack plus another smaller pack strapped on is enough for a week away for me.
Also I have a 10l bag which is OK for day rides.
I like it because it is well made and fairly unobtrusive when underway - (it doesnt stick out) also it is quite a bit cheaper than the hard luggage.
Obviously not as secure as hard luggage though.
A helmet fits in the 45l pack no problem.
Swapping of packs and frames is easy.
Grant.
the pack can be put on around the other way if you have a pillion.