Human Hair is like a tree...it has a cuticle on its outside to protect the inside of the hair just like the bark protects the wood of a tree. On the inside human hair has a cortex, just like the wood of a tree.
Most hair extension brands strip their hair's cuticle with acid exposing the core of the hair or cortex. Their hair is then bleached, dyed, and dipped in silicone at high pressure, for temporary silkiness & shine.
The problem is, the silicone lacquer washes out days later, the hair looses it's shine and begins to crack & tangle terribly.
Many companies actually use animal hair from the Yak for inexpensive long hair. Then they take the coarse Yak hair, strip off it's rough cuticle with acid and stretch it with perm lotion for length. Then they bleach & dye the animal hair & lacquer it with silicone.
They still sell that to you as 100% Human Hair.
Many other companies add 20-30% high temperature resistant synthetic fibers to their extensions, and still have the nerve to call it 100% Human Hair!
That's the reason why the extensions look like a mop after a couple of washings.
More info: http://www.organichairextension.com