These threads are "bonded" or treated with a liquid resin and then cured and lubricated.  The bonding prevents fraying at the cut end, helps resist untwisting tendencies and protects the thread from abrasion and heat damage in the needles of high-speed sewing.

Coats Threads

Dabond 2000 UVR Polyester thread is ultra-violet and mildew resistant, bonded for smooth running through machines and has a high tensile strength with low stretch.  Great sails and outdoor applications.

Conso Threads

Sunguard Threads