Verified answer

I haven't actually had a piggy back perm, but I've done them. They're the same as any other perm only they use two perm rods per strand instead of just one. They're reccomended for people with long hair that want a perm. Basically the hair is too long to roll right on just one tool so it gets rolled half way from the end to the roots & then the next tool brings the ends up. Your hair will look no different with a piggy back perm then it would with a regular perm, it will just take a little bit longer to roll

they are for really long thick hair -you use one rod on the top half of a strand and one rod on the bottom half of it. It's basically a spiral perm - I used to get them done by my mom for years when I was a kid.

it's where your hair is long and it takes two perm rods on one strand of hair.

http://fc.bcps.k12.va.us/~ppratt/