How do you call that kind of hair extension where they melt something that connects the strands to the hair?

i saw it on tv and the styler inserted a bunch of strands on a rubber/plastic tube and then inserts it to the real hair and applies heat (scissor-looking contraption) to melt the tube to connect it to the hair.How do you call that kind of hair extension where they melt something that connects the strands to the hair?
It's called hair fusionHow do you call that kind of hair extension where they melt something that connects the strands to the hair?
bonding
It's bonding. And it can be a very expensive process!