Originally Posted by cgaengineer
Wasn't making fun, just don't believe it...and still don't.
You can believe what you want, but you will still be wrong.
This has been VERY well studied in the field of tournament fishing, where nylon monofilament dominated the field until newer lines came out, and the effects of water absorption are pretty well understood.
Here's a decent technical explanation of what's happening:
"Nylon monofilament is a lot like spaghetti—it absorbs water in copious quantities. Trying to pull a piece of dry spaghetti apart end to end is tough, but as soon as it gets cooked (i.e., it has absorbed a bunch of water) it pulls apart with ease. That’s an extreme example, but you get the picture.
In reality, nylon monofilament will absorb up to about 10% of its weight in water. Water absorption is a mixed blessing. On the upside, nylon monofilament that has absorbed water becomes more limp and supple, and makes knot tying easier. On the downside, water-logged nylon monofilament swells, increasing its diameter, reducing its break strength by about 20% (i.e., 10-pound test becomes 8-pound), and increasing its elongation (stretch) by 25% to 30%."
Professional competitive fishers have been soaking their line in water (and sealing it in wet zip lock bags) for a long time now, as it gives an edge in competition.
In the case of string trimmer line, the cheapest lines are simply pure nylon monofilament (just like plain old timey fishing line), while some more expensive lines include aramid for greater strength as well as shock resistance, plus resistance to welding.
By soaking the string in water, it may have a lower tensile strength, but the weight increase gives it more momentum at the tip, which causes it to cut more while flexing less. This will make it last longer.
Also, the additional stretchiness will help it flex at the eyelets without breaking.