About to start Dreads and need to know if i can use synthetic hair to mix in with my real hair to make my dreads longer ?
Dreading Methods
I would not suggest synthetic hair, if human hair is a possibility...
1. You have to start over completely if you want a new haircolor.
2. Some people (myself incl.) get weird acne on the back from synthetic hair. (seriously dont ask me why, it's freaky). Would suck to do all this work and end up with that.
3. It's will not be reacting to products, time and so on like your own hair, which could be a real pain after some time. Imagine having the first half of the dreads looking awesome, and then the lower part looking completely different :-S
I know synthetic hair is cheaper, than human hair, but maybe do as I did, and just ask around if any of your friends have old extensions lying around, that they know they wont be using again. You would be surprised to know how many girls keep it, and are happy to see it being used for something good. The older and more ruined the hair is, the better it dreads 
I have 50 cm of extension dreads and paid nothing for the hair. (I had some myself, but most of it I got from friends)
If you want the possibility of dying the hair, try getting blonde hair, and use hair dye in your own color. I learned this the hard way. The dye they use on the extensions at the factory, is not normal hair dye and some of it can not be bleached even after lying in bleach until it fell apart. When I wanted to go blonde, I all of a sudden had 18 ugly brown thingies hanging in my hair, that I had to replace, which was shitloads of work... Just happy that I only used dark hair for those, if it had been all 80 I would have died a little inside...
I added my length in two rounds. One in january while I was making the dreads, which gave me a typical little longer than shoulder lenght. The rest I added a few weeks ago. The reason is that your head needs time to get used to the weight. I've heard about girls who had hair falling out, red dots all over the scalp and so on. Further more even 100 gr of extra hair will make your head feel heavy.
As for the method, I tryed some different ones, until I found what worked best for me.
BTW I fucking love my very very extended locks! I mention this, because everytime someone tries asking about things regarding dreadlock extensions, someone comes roaring in to "save" the day, with comments about how wrong it is to have extensions, which is in good heart, I know that, but unfortunately, it means that people like me, don't feel welcome in here. In the last five months I've only felt judged for my hair once and that was when I tried to join this community. As many others (I later realised from other forums around the web, which unfortunately are so much smaller than this one) I just left, with no intention of returning, but EVERY time I try googling a question on my hair, this page is what comes up. Which would be fine, if not for the fact that half the time the answer to peoples questions are not really being answered because it is oh so important to point out that extensions are baaad and probably also because people who like their extensions, either doesn't use this forum or maybe aren't the types who like disagreeing with the top dog...
Today I guess I kinda snapped, because hating online like this, is really not my style, I just needed to get this crap out there, to be honest it has been eating at me for this whole time, because it was my only bad experience with dreads and really made me feel sad at that time :-/
And boy, could I clone her dreads I would