As always do your research, some companies and websites recommend using anything from clear nail polish to fabric hot glue? So to be safe, look for bonding glue sold specifically for weft bonding. There are a few brands on amazon.com. Be sure to follow the instruction provided on the bottle.
Once you have the WEFT glue you want to use, lay the wefts on a flat surface. Be sure you cover that surface to prevent damage. “Surgically” Apply the sealant directly to the weft of the hair, just as you would if you were going to “glue” or bond the hair instead of sew-in installing the hair. Allow the WEFT glue to dry completely before installing. DO NOT allow WEFT glue to touch your actually hair. The package instructions will detail how long you should allow drying time to be. If you live on the wild side or are impatient, you can blow-dry for a quicker result. Be sure to apply WEFT glue to both sides of the weft.
Of course, you didn’t just do all this extra bonding and sealing business for nothing. Be sure to re-seal or have your stylist re-seal any cut wefts ends with the WEFT glue.