Watty is right on his input - lines are part of the way your kite works, in the way you're looking for! I use the line that came with my Wala, for my Plutz, Mega-Plutz and Frigate (Skate style glider)! Then I use an LPG made fly fishing leader material for all my small gliders -iFlite and iFliteII!! I also use a small swivel to take out line twists and it adds just a bit of weight!
I'm not big on using LPG, myself! I feel that it will "bite" into your skin if it moves too fast through your fingers! I've eliminated that by using a wand with all my indoor gliders!
The heavier line changes the glide for many gliders, it can be used instead of added weight in the nose!
Outdoors, I found that fly line backing does the trick! Comes in several weights and colors! Got 2 weights 20# + 30# in different colors to keep them straight! Still helps to wear gloves with it though, too much movement causes line burn!! Might try some fighter kite line sometime to see if I like that!!
It's all in what you are looking for and how you are going to use it!!