The Seymour Duncan Zephyr series of pickups was introduced in 2011. They have several unique features including:

• Silver wire coils. Silver wire is a better conductor than than the traditional copper wire used in guitar pickups. This means that for a given number of turns the coil's resistance is lower, although this is unlikely to have much of an effect on tone. Silver wire is more "bendable" than copper wire, so the coil will be wound more uniformly and tightly: this means less microphonic feedback in non-wax-potted pickups.
• Nickel and stainless steel bi-wetallic pole pieces: this is an interesting development designed to improve the pickups magentic properties- exactly how I don't know.
• Cryogenically treated. This supercooling can make the crystalline structure of metals more regular, thereby increasing strength and decreasing electrical resistance. There is a possible audible effect on tone.
• Glass Fiberfill Nylon Bobbin: Everything else about this pickup is high end so you couldn't just have a regular plastic bobbin. The glass-fiber reinforced nylon has slight advantages of definition, detail,stability and consistent finish compared with the regular bobbin material.

The people at Seymour Duncan are convinced these are their best sounding pickups:

" Zephyr Silver pickups uniquely fast transients, wider but smooth frequency response, deeply rich harmonics, and unprecedented midrange tone density, with audible gains in string detail, articulation and overall definition. Slighter touch produces expressive sound, yet peak dynamics are more explosive, making your guitar feel more energetic and alive. We consider Zephyr Silver the most expressive pickups so far. They are not inexpensive, but from squeaky clean to buzzsaw grind, you'll hear and feel more power, projection and expression from any electric guitar."

If you're interested in cryogenic pickups also check-out ChillerTone - they can provide cryogenically treated Seymour Duncan pickups

Link: Chillertone cryogenic pickups