Sewn-in Wefts
The sewn in weft is one of the most used out of all the extension methods. It is the most versatile and the gentlest, provided it is done correctly (but then that's true of all the methods).
A continuous track is made so that the whole track works in unison to hold up the weft as a whole rather than creating stress points like in the example below.
This method will create stress points and cause breakage
With sewn-in wefts, there is no heat necessary. They last 3 months before needing to be tightened and the hair can be reused as many times as the hair quality will permit.
The sewn-in weft is an excellent way to get a lot of hair in quickly (it takes 30 minutes to put in a weft which is equivalent to approx. 100 individuals) to create a base for other methods or can be used on its own to create a full head.
This method is one of the safest ones for the natural hair and a favorite of mine.
20 minutes is all it takes to sew in a weft and once in the hair you'll get no slippage and definitely no breakage.