For one of the strongest, most un-natural, shiniest, synthetic yarns around, you can't beat polypropylene! It's great value for money, comes in bright colours and can actually be used for lots of
Polypropylene Yarn Construction Rope (Large Coils) - Kendon Rope and Twine
Polypropylene – DFW Thread
Polypropylene Yarn in various colours - tough, strong and great for outdoor, macrame and crochet projects or just something different
Coats Prolene Teabag | Polypropylene Thread for Tea bag Manufacture | Coats - Coats