I myself bought a terrible filament from reprapworld.com - small spools - much tension, and later after the filament started to just crack into small pieces. Heating up the spool in an oven releaved the tension, but made the filament even more wavy, it caused some jams, it was hard to pull the filament from the bowden by hand. And I bought 10 kilos from them, nevermore.
But I found a good and reliable way to resolve this issue. I have an aluminum cylindrical pot, with a comparable to spool diameter, 25 cm tall, what I do is wind the filament onto the pot, fix it with tape and heat in oven 50