What material are the knots made out of to give them that effect when the lights are shining on them?

I don't believe that the knots are glowing because a light is shining on them. I think they are knot-shaped constructions with lights embedded in them. Like a lamp that just happens to be knot-shaped. That said, last winter I bought some decorative lights (a flexible transparent plastic tube with LEDs inside) on sale after the season was over and was planning to tie it into a knot. Reading the safety disclaimers about heat and the possibility of the whole thing bursting into flames if it wasn't hung out straight dampened my enthusiasm, but maybe this year I'll try tying it and take some pictures before it bursts into flames. 8) 8)