• Key-hole Bridge
As the name implies this bridge style found on plastic frames is shaped like a key hole. It should fit such that the sides rest on the nose but the center rests above the nose. This shape is used to accommodate people with a thinner bridge of the nose. Again, this bridge must fit well from the start

• Spring Hinges
This is an excellent feature which helps make frames more durable. The spring mechanisms, located in the temple hinges, help the frame maintain adjustment through normal use and give some added durability if they should get some excess wear.

• Cable Temples
This type of temple wraps around the ear and holds glasses securely in place during all kinds of physical activity. This is an excellent option for young children. With this option the glasses may be more difficult to take on and off.

• Seperate Nose Pads
This is the most common nosepad configuration of metal frames, with two separate nosepads attached to the frame on metal arms. This design allows for a more custom fit to the nose and helps to keep the frame from resting on the face.

• Unifit Bridge
This one piece bridge/nose-piece, on a metal frame, distributes the weight ofthe glasses evenly over the nose. However, if this nose piece style does not fit well to begin with, it usually can not be adjusted. There is an adjustable type of unifit bridge but its range of adjustment is limited.

• Saddle Bridge
This bridge style found in plastic frames, spreads the weight of glasses evenly across the nose. It is important to note that if the bridge of a plastic frame does not fit well in the beginning there is little that can be done.

• String Mount Semi-rimless
This term refers to frames that go partially around the lens. The lens is held securely in place by a nylon cord. Rimless frames are good for those who don't want to see as much rim of their frame.

• Drilled-rimless
In this type of lens mounting, The lenses actually have holes drilled in them and are fastened to the frame assembly with screws. The affect is a minimal amount of frame. However, this is the least sturdy type of frame and more maintenance may be needed as screws may loosen and the edge of the lens is exposed all the way around.

METAL FRAMES

• Pure Titanium
This is a premium frame material. Titanium is stronger, with twice the tensile strength of traditional metal frames and is 48% lighter. Titanium is also 20 times more resistant to corrosion and is hypo-allergenic, due to the fact that it is nickel free.

• Stainless Steel
Stainless Steel is made primarily from Iron and Chrome. It is a very strong metal alloy. Stainless steel frames can be made veryÊ thin and still maintain their strength and flexibility. Like Titanium, it contains no nickel, therefore it is virtually hypo-allergenic and resistant to corrosion.

• Memory Titanium
"Flexon" is the most common trade name for this frame material, which is a mix of 40-50% titanium and 50-60% nickel.This metal is extremely flexible and offers excellent durability. It is most commonly used in parts of the frames such as, the bridge and temples, where such qualities are needed most. (These are the frames you may see advertised twisted around a finger without breaking)

• Beta Titanium
This is a titanium alloy, utilizing combinations of titanium, vanadium and aluminum to create a flexible, durable, lighter material that is nickel free. Because it is not 100% titanium, its cost is usually lower than the pure titanium frames.

• Cobalt Alloy
Cobalt alloy frames offer the benefits of being lighter as well as being hypo-allergenic. Although they are less expensive than their titanium counterparts, they are not as strong and durable.

• Monel
This is the traditional metal used for frames. Monel is an alloy containing nickel, copper, iron and other trace elements, with nickel being the primary component (at 63-70%), followed by copper and then iron (at only 2.5%). This material is pliable making it easy to adjust. It holds its finish well, however, it is more susceptible to corrosion and more apt to cause allergic reactions due to its high nickel content.

• Aluminum
While aluminum was popular at one time, and is strong and light, it is not used much, as it does not solder or weld easily and is difficult to adjust.

PLASTIC AND OTHER MATERIALS

• ZYL
This is a term used for a variety of plastic materials used in makingÊ frames, the most common of which is Cellulose acetate. Cellulose Acetate is made from a cellulose material extracted from cotton or wood pulp mixed with anhydride acetic acid, plastisizers and aging stabilizers. This material can be shaped into frames in two ways. It can be formed into sheets from which frames are stamped, or it can be injected into frame molds. It comes in a veryÊ wide range of colorsÊ with good color stability and is easily adjusted. Some people haveÊ had allergic sensitivity to zyl frames. This is less likely with high quality zyl frames, which usually have an additional protective coating that prevents fading and UV damage to the frame material.

• Optyl
Optyl is the trade name for an epoxy resin which is drawn into molds while in its liquid state to make frames. This material is "thermoelastic" meaning it will bend when heated but will return to its original shape when heated again.Ê This quality does make the frame more apt to come out of adjustment if exposed to hot temperatures (Such as getting left in a hot car!).

• Co-Polymide
This nylon based material is quite strong, can be made thinner and is approximately 30% lighter than traditional zyl frames. Co-Polymide is available in a wide range of colors. It is resistant to chemical damage, and is hypo-allergenic, however it is also somewhat resistant to adjustments.

• Carbon Fiber
This material is made by combining carbon fibers and nylon and while this creates a thin strong material, it is not adjustable. Carbon fiber is most often used in frame fronts, in combination with metal temples, however remember if this frame does not fit properly in selection, it will not be able to be adjusted any better later!

• Nylon
Nylon is a highly flexible material, because of this fact, it is most often used for sunglasses or sports glasses. Nylon, however, does not hold an adjustment well so initial fit is important. To maintain flexibility, frame should be soaked in water overnight periodically.

• Polycarbonate
Frames made from polycarbonate are associated primarily with sport or safety uses. Polycarbonate is often used for nonprescription shields, where the lenses and frame are molded in one unit. It is also the material used in the type of sports frames held on with elastic straps. In combination with polycarbonate lenses, this material offers optimum impact resistance and eye protection. This material can not be adjusted.