Can you flat iron synthetic hair?

No, synthetic hair isn't heat resistant. You can only flat iron human hair extensions (like Easy Clips hair extensions). There are some synthetic hair extension brands that are heat resistant but it has to SAY that it's safe to heat style them.

You can straighten them without heat by soaking them in hot (not boiling) water and then making sure they dry while slightly stretched so they're flat. You can TRY to use a flat iron on them but only on the lowest heat.