Keratin tips are also known as hot fusion extensions. Because the glue used is made of keratin, the same keratin found in hair, it is very compatible and gentle on the hair.  

 

They are applied to the client's natural hair in small 'bundles' with a heated keratin adhesive.

 

Since your hair is already made of 90% keratin (a protein compound,) this method is actually gentler on hair than regular glue is.

 

These will last up to 4 months and the hair can only be re-used once and that is if you are willing to go shorter since the tip has to be cut and a new keratin tip applied in order to be re-used.