Spirit River calls their material UV2. I think the "2" in UV 2 refers to UV Fluorescence + UV Reflectance.
From a Spirit River UV2 Advertisement :
"The UVR spectrum is extremely common in the animal/insect world. This is how bees find flowers and mayflies find mates. While many male species exhibit UVR to attract mates or to feed, many females exhibit less UVR to camouflage themselves and their young.
UVR is abundant in plankton, algae, baitfish, invertebrates & similar species. UV sensitive cones in the eyes of fish allow them to see in much greater detail in adverse water and light conditions......
Our special UVEM™ dye processes on feathers and furs add more UVR by increasing its electron mobility, its luminescence and overall light spectrum. The UVEM™ is high in reflectivity and has diffusing properties, which the animal world identifies and exploits. With a special UV light held behind a material, the lighter shades (red and above) will glow ever so slightly.
A better way of saying this is that our fluorescent materials “scream” at you and our UVEM™ materials “whisper” to you."
I don't doubt that Spirit River UV2 materials are effective. However, they imply that somehow they imitate the UV reflectivity of natural bugs. Notice that they don't actually say their UV reflectance matches bugs or bait fish; but they mention it, and they want you to make the logical leap that they cannot state.
If I wrote that aquatic insects reflect visible light and that I had dubbing for sale that reflected visible light, you would say, "So what!" The fact that my dubbing reflects light does not mean my dubbing MATCHES the color of the real insects. No where in the ad does it say that the Spirit River material actually matches the UV reflection of insects or baitfish. Just as in the visible spectrum, there are specific UV colors(wavelengths). To actually imitate the UV reflectivity of a food, the tying material has to reflect that UV wavelength and no other!
That leads to my belief that the Spirit River materials work primarily by fluorescence. By mixing fluorescent material into dubbing and adding fluorescence into natural materials, I think the Spirit River materials increase the visibility of flies tied with their materials.
If UV reflectance was the main reason they worked, we have been using a highly reflective UV material for decades. That is mylar tinsel. Mirrored materials reflect both visible and invisible light from infrared to ultraviolet.
Sun worshippers used to use these back in the 1960's to reflect both UVA and UVB radiation that causes stimulates melanin production and skin tanning.
I suggest this article on UV reflective and UV reactive (fluorescent) tying materials. Read the comments section as well. The comment by 1M1Ucla pretty much mirrors my thinking on the subject.
Shining a Light on UV Materials | MidCurrent
Reed Curry wrote a book on Trout and UV Vision and by extension promotes using UV reflecting materials for fly tying. The problem, as I have mentioned in the past, is how do we know what UV “color” to use when we cannot pick our the right “shade” of UV because we cannot see into the UV spectrum.
Read the comments on this blog to the interview of Reed Curry.
Ultra violet fly tying materials catch fish, Q&A with author Reed Curry | The Caddis Fly: Oregon Fly Fishing Blog