20 or 30 Volume Developers?

I'm just curious about something. I've noticed that Volume Developers range from 10% to 40% and I'm wondering what each percentage can do for your hair color, and what % should you use for what situation?

Many of us hair coloring amateurs assume that the higher the %, the higher the color lift you will get, but I have read that that doesn't necessarily end up being the case, and all you may accomplish is very damaged hair the higher you go on the % of a volume developer. Can someone please educate me on this. Thanks so much!

I have blonde hair but it has become darker over the years. I use a mix of 20 and 30 - equal parts - and it lifts better. If you start out darker, you'll have to use 100% 30 volume. You might want to do a test strand to see the results before doing the entire head. Also, if it is harder to lift, you'll need more time. I think 40 minutes for 30 volume and 30 minutes for 20 volume. Of course, you have to just do the new growth or the 30 volume will damage your hair if used over and over again, so will 20 volume for that matter.