ho ho brother.. since u say it's flexible even you didn't heat it. .. sure it will melt if u put in ur headlamp or spot light..
This is because that is a glue gun rod, I think you have misunderstand already with the stuff..
The transparent thing you refer is the Acrylic Round Rod, which you can get it in Jln Pasar where there is a shop called Acrylic Shop.. When you go there you can see got round transparent or hexagon transparent rod. It come with straight line condition and when you need to make it like Angel Eyes, you need little heat to bend it ..
If you saying the glue transparent rod which you can bend even you didn't heat it up, then that is not the one you can make Angel eyes..
Let say if you have the proper material to do angel eyes, it is not so easy to melt it under the hot sun.. I have installed into my car headlamp for few months already and just dun care put under hot sunny place.. and doesn't have change to different shape... Provided you give spaces when you put the angel eyes to have some air circulation, then it should be fine.. = )
Hope this helps..