Gonna quote myself from another thread,
It can melt, but I've had luck straightening both pearly and metallic tinsel. I tend to straighten all the hair first, then grab a chunk of hair (properly wet with conditioner) and some tinsel and run it over fast with a travel straightener. So far I've never had anything melt, unless I've accidentally clamped down on it for too long, although I advice caution with this, and to use a low-heat iron/setting.
Good luck
Be quick, and careful, and it should work ^^ Be extra careful with pearly tinsel though.