For one of the strongest, most un-natural, shiniest, synthetic yarns around, you can't beat polypropylene!
This stuff won't rot, won't stain, won't fade (unless exposed to 1000's of hours of sunlight), won't absorb any moisture, is difficult to burn and actually has great thermal properties. It's great value for money, comes in bright, clear colours and can actually be used for lots of things!
Our range includes a yarn often braided and knotted into cords, ropes, plaits, though if you are feeling adventurous you could knit or weave it into fabrics and garments. It has an acetate floss type appearance meaning there are hundreds of tiny threads making up the yarn (rather than two or three thicker ends), so for tassels these would puff out and drape brilliantly.