Fusion, Infusion, Strand by Strand
Extension hair is applied strand by strand (Infusion) with a hot or cold form of adhesive. The adhesive can be a keratin based product or other natural-based products that can be very similar to the material that makes up the hair and nails and is considered to be non-damaging to your own hair. Some companies will vary the amount of individual pieces of hair that are included in each strand. I.E. some will consider 20-30 human hairs to be one strand.
There are many types and variations of adhesives available, including waxes and medical grade adhesives. Extension hair applied in wefts is called fusion and extension hair applied strand by strand is called infusion.
Lord & Cliff
Super Hair Factory
Generally speaking, fusion refers to both strand by strand and weft attachment. Fusion is a more permanent technique that can last anywhere from 3-5 months. Be advised that there are some stylists and professionals in the hair extension industry that stress that no hair extensions should be left attached to your hair for more than 8 weeks, as they will cause permanent hair loss if left on longer. (Called traction alopecia)
Follow each link for detailed information about each method and the hair extension company websites.