100 wt. monofilament polyester thread. Designed for invisible applique and quilting. This reduced-sheen monofilament polyester is the best choice when it comes to invisible threads. Unlike other monofilament threads made from nylon, MonoPoly is 100% polyester. Commonly referred to as an invisible thread due to its fineness and reduced-sheen, MonoPoly is great for the bobbin or top. Clear is best used for light or bright fabrics.