Here's an example of 60-65% density. This is a short hair style and if you want a longer hair style 60-65% could be too much hair. You might want to go with lesser density for a longer hair style. And remember: you want the density of the hair piece to match the density of your own hair on the back and sides.
John
http://toplace.com/

Why would a longer hairstyle be too much hair? I'm young and was planning on doing at least 70-80% density and my style would be several inches longer. Would there a problem for me doing that?

NoHairNoFair,
When you get longer hair you get your volume by the hair length. When it's short you need more a little more density. Sebtizzle, remember that you want to match the hair density of the hair system to your sides. I'll bet you have good density on your own back and side hair. And you're right about needing more density if you're adding gel or wax to the hair system as those products take away the 'fluff' in hair.
Regards,
John
http://toplace.com/

What about someone who has thinning sides and back (like me!) and who is not interested in a full cap unit? I see many styles where the sides and back are really short with lots of hair on top.

Anybody wear a unit like that?

Oldwearer.