Most invisible monofilament thread is made from Nylon. There are only two reasons why Nylon thread should be in your sewing kit.
Bonded Nylon is a spectacular fiber for upholstery and heavy-duty stitching. Superior's Bonded Nylon is made from a special type of raw material called Nylon 6,6. Nylon 6,6 is strong and the bonding agent which coats the thread adds strength and reduces friction when sewed at high speeds.
Fusible Thread, such as Charlotte's Fusible Web melts when exposed to heat. This is a great thread for temporarily adhering appliquéd pieces onto backing fabric.
Here's an explanation of Nylon vs. Poly
Nylon thread should not exist in your sewing supplies unless you want the thread to melt. As strange as this sounds, this is very true. Nylon threads, whether they are woollie-type threads which are used in sergers or invisible monofilament threads, have a very low melting temperature, discolor or "yellow" over time, and go brittle. Polyester threads are much better to use than Nylon threads.
Fusible Thread is Nylon, made to melt. MonoPoly is an invisible Polyester much like the Invisible Nylon on the market, but with much more added benefits. Polyester threads exist in both the woollie-type for sergers and the invisible monofilament. Polyester has a high heat tolerance, will not discolor, or go yellow.
One more thing to check: If your monofilament thread is labeled "polyamide," that is not polyester, but the chemical name for nylon. Don't be fooled.
Superior Threads does not carry a Nylon Invisible Monofilament thread. We don't use or recommend it. Our Monopoly is Polyester and therefore is dryer safe, won't yellow, won't go brittle over time, and can be ironed on a lower heat setting. We suggest using a Polyester Invisible Monofilament thread over Nylon for these reasons.