We're talking Polycarbonate lenses here, folks.
What is Polycarbonate material?
Essentially, we're talking (in the context of Shooting Sports) about frames and lenses which offer an unique combination of lightweight, non-intrusive sunglasses which not only cut out 100% of ultra-violet light, but also are extremely resistant to shattering under the impact of a bullet, parts of a bullet (jacket, etc.) or debris such as rock chips.
Polycarbonate lenses are thinner and lighter than traditional plastic eyeglass lenses. They also offer 100 percent ultraviolet (UV) protection and are up to 10 times more impact-resistant than regular plastic lenses.
Polycarbonate was developed in the 1970s for aerospace applications, and is currently used for the helmet visors of astronauts and for space shuttle windshields. Eyeglass lenses made of polycarbonate were introduced in the early 1980s in response to a demand for lightweight, impact-resistant lenses.
Since then, polycarbonate lenses have become the standard for safety glasses, sports goggles and children's eyewear. Because they are less likely to fracture than regular plastic lenses, polycarbonate lenses are also a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.
In a word: eye protection.
Okay, that's two words.
How "good" are Polycarbonate lenses in terms of protecting your eyes from injury?
A few years ago, the "Front Sight" Magazine ran an article which compared the then-state-of-the-art glasses from a number of vendors using a variety of materials. The Polycarbonate lenses resisted shattering under the greatest number of assaults, including bird-shot from a shotgun, a .22 caliber rounds, and small-caliber pistol rounds.
(Trust me, if you get shot in the eye at appreciably close range from almost any kind of gun, you will end up looking like Johnny Depp as "Agent Sands" in the closing scene of "Once Upon A Time in Mexico" ... blind, and bleeding copiously from your empty eye socket. We're not talking 100% anytime, anywhere, anything protection here. We're just hoping for a reasonable degree of protection from splash-back, which IS possible.)
Polycarbonate is not perfect.
A couple of years ago I bought a pair of reading glasses and specified Polycarbonate lenses. I discovered that the material was not appropriate for daily use. After less than a year, the glasses were scratched by the wear caused by the (plastic coated) bows as they rode in the glass case.
On the other hand, I once (accidentally) drove my Jeep Cherokee over a pair of Polycarbonate shooting glasses in an asphalt parking lot. The glasses were, predictably, seriously scratched. but the lenses were not broken, shattered, or otherwise compromised as far as the overall integrity of the lenses was concerned. These were Silencio "SD" glasses. (See below)
Today there is a much more scratch-resistant material available: I don't have the link yet, but they are stronger, and they cost more. A lot more ... say, 2 to 10 times as much for the material. (I bought new reading glasses glasses this year, and with the cost for grinding the lenses it's hard to tell how much is spent for the material.)
Here are three glasses types using Polycarbonate material (click on the images for full-size):
Silencie SD: Original cost, about $12.oo
Silencio Nemesis: about $10 if you can find them in your local gunshop
Personally, I like the Claypro glasses the least, because the wire frames seem more likely to break under constant hard usage.
The heavy plastic frames of the Silencio glasses seem more durable, but perhaps that's just the Buddy Holly in me.
All of the glasses pictured here feature Polycarbonate lenses, rest on the ears and nose bridge without touching eyebrows and cheeks, and offer varying degrees of "wrap-around" protection.
Also, they look pretty weird. That may be a selling point to you; it is to me.
Note that there are a few things to avoid when shopping for shooting glasses. The most important is that the frames shouldn't be heavy, because the become uncomfortable and they tend to droop (as you do) by the end of the day. If the frames are reinforced with extra material which may cause them to touch your forehead, this will soon become unbearably uncomfortable, and may in fact encourage sweating on hot days. Similarly, frames which touch your cheeks will not rest easily on your face for the length of a summer's day.
Note that I also looked at S&W frames. They seemed similar to the Silencio, if more expensive. I saw no added value for the price, but seemed more widely available. If you can't find Silencios, these S&W glasses will probably provide similar protection and comfort, if at a greater price.