It's pretty important to stick with name brands and either Spectra or Dyneema(Europe). It's also called ultra high molecular weight gel spun polyethylene. It's a pretty fussy process because the temperature of the plastic is highly critical. The polyethylene is extruded through a very small die and stretched rapidly while it cools. The process makes the long chains of the polyethylene(high molecular weight means long, unbranched molecules, some 400,000 atoms long) line up very tightly packed and all forced very close to each other. The individual strands are gathered into bundles of several hundred fibers and the bundles are braided into the line. The result is a cable as strong and resistant to stretching as high strength steel, but only 1/7th the weight. Depending on how it's braided in may be slightly draggier than steel lines. On the plus side, besides being easy to tie to an exact length it won't tangle itself up, kink, or fatigue and break from vibration, or get damaged by a Big Foot tripping over your lines.
Since it's made entirely of polyethylene which melts at 275 F the line shouldn't be exposed to temperatures much over 150degF, certainly not high than 175-212 degrees. When the strand gets too hot the molecules can lose their straight line orientation and get more loosely packed loosing most of their strength. For similar reasons it's easy to make mistakes in manufacturing that give the same result- a stretchy, low strength strand that's useless for flying models. You won't know a low cost knock off will work until you get it home and test it with a pull tester. If a 60 ft. line stretches more than 1.75-2in with a 25lb. pull test it's too stretchy and is not the right material.
Fly until you've had so much fun you fall over,
Phil C