Thermal Hair is made from saran or polypropylene fiber that changes color in reaction to changes in temperature. It comes in small packages ranging from 22-25g, which is enough for a couple braids or thin highlights.
Thermal hair has a higher resistance to heat than kanekalon, but can still be boil permed and will melt under high, dry heat like a straightener/flat iron. Boiling water generally is not hot enough to seal it. It will not shrink when sealed, but will hold its shape once set.
If the ambient temperature of the room you're in is close to the point where the color changes, sometimes it will appear to get "stuck." For example, your hair might be purple in the bag, turn teal from the warmth of your hands when you remove it, then stay teal after you've set it down. You can get it to go back to purple by exposing it to a much colder temperature, like an ice pack.
The temperature that causes the color to change varies by color; if you are using multiple colors together, they will not all change color at the same temperature.
Thermal Hair cannot "burn out" - the fiber will never stop being able to change colors.
Thermal has has very fine and is prone to tangling, so it's important to be careful and gentle when separating it. We do not recommend wearing thermal hair loose. We also recommend doing an ACV rinse before installing; it can sometimes help a bit with the tangling.