fiberglass?

The fiberglass adhesive I've used is an epoxy, very permanent and resistant to solvents. Also, it gives off toxic fumes - nothing I'd want on my scalp or hair, or in my lungs. Hopefully they are using a safer product than that.

I looked at the website. Although they claim the process is completely safe and harmless to your hair, they didn't talk about how the extensions are removed. I wouldn't go anywhere near that place unless you could get lots more information on safety and removal in writing.