From what I understand, Ultex, just like Ultem, is simply a brand name for polyetherimide (a.k.a. PEI (not to be confused with polyethylenimine, which is also often referred to as “PEI”)), a high-performance thermoplastic, used in medical and aviation industries. Knowing this fact, the durability of the picks comes as no surprise: these are by far the longest-lasting picks that I have ever tried. If you manage not to lose them (which is not that easy to achieve due to their transparency), they will easily last you for months — if not years! — depending on the individual circumstances. I usually use them for about a year before the tip becomes too blunt for my liking; which is incredible considering that I practice for at least two hours every day and use 12-gauge strings. Thanks to the rigidity of these picks, the transient is always perfectly clear, and I always feel in control of the situation, which is especially great for soloing. The only drawback for me (besides them being close to impossible to find on the carpet) is the annoying clicky sound they produce upon hitting the string. I am used to holding the pick as close to parallel to the strings as I possibly can, so the clickiness is even more perceptible. It cannot, of course, be heard through the amplifier, but when practising unplugged in a quiet environment, it can sometimes become overwhelming. Red nylon Jazz IIIs do not do this, but they wear significantly faster and, unlike their Ultex counterparts, always have molding marks around the perimeter.