It seems pretty simple, do you want a plastic or metal frame....
But! If we dig a little deeper there are far more options for frame materials and preferences than you probably first thought.
Metal Frames
Lets start with the metals first. No 2 metals are exactly alike when you compare them and all their features! As metal can be corrosive to most skin types, a metal frame should never be touching your skin, even if you don't have an allergy or sensitivity to any metal that you know of. This is why metal frames will always have the nose pads on them, and will usually have some kind of plastic tip on the temple area that bends behind your ear. However, some metals will be better than others. Here is a breakdown of a few of the most used metal materials in frames:
- Nickel blends: Most of the very affordable and easily accessible non name brand (and some name brand as well) will use a Nickel blend of metals. This blend is a bit of a mystery, as it can have varying percentages of nickel content mixed with other metals like copper, steel or chromium. This can be very difficult to repair with soldering as the higher the nickel content and the less steel content in the blend will not hold a solder repair. This is also the material most likely to cause an allergy or sensitivity response in people who wear them. Nickel blends can have varying degrees of strength and lasting power. The higher the nickel content in the blend, the more likely the metal will degrade and soften over time, and then more likely it will break when the metal does soften in this way.
- Stainless Steel: Stainless Steel frames are going to be light an comfortable, are easy to adjust and are strong to holding their adjustment. Some people may still have a slight allergy to a steel frame, but it is fairly rare. Stainless Steel is also very repairable with a solder if a breakage does occur, as long as it is not blended with any nickel content. They tend to be a more rigid material which feels secure on the face and will hold its adjustment pretty well over time.
- Titanium: Titanium is the lightest of frame metal materials and is a hypo-allergenic metal, so it is extremely unlikely you would ever have a reaction to it, even if the metal does touch your skin. You will notice some Titanium frames will not have the plastic temple tip cover (as
mentioned above) like other metal frames, this is because it will not corrode and react with your skin and facial oils like other metals can and will do. Titanium can come in a pretty rigid material that feels pretty sturdy, but can also come in a flexible or memory titanium which bends and moves without breaking in exceptional ways. The one downside to a titanium frame, especially if it is the memory or flexible version, is that it can be more difficult to adjust as it wants to pop back into its natural bench straight adjustment. This is a concern more for your optician than you, as your optician will know the right method of heating the frame in the correct way to be able to hold your custom adjustment. Once they have been adjusted correctly though, they will be some of the lightest and most comfortable metal frames you will wear that will hold the custom adjustment for a very long time!
Plastic Frames
Many people prefer a plastic frame over a metal frame, them main reason for this is some people just do not like having nosepads on their glasses. Although some plastic frames may have an option to have nosepads added for those who want the look of the plastic frame but prefer the nosepads, most plastic frames will not have this option. The most important thing with plastic frames is making sure that the bridge fit is exact, as any 
discrepancy in the bridge will allow the frame to slide down your nose, no matter how tight they are adjusted for you. Another thing to keep in mind is that plastic frames tend to be a bolder look and have a heavier feel than most metal frames, so if you tend to be more weight sensitive on your bridge or like a very minimalistic frame style, the plastic options may not be your best choice. Plastic frames also do tend to widen up more over time than most metals do, especially if you wear them on top of your head when they are not in use. For the record, a good optician will always advise you to NEVER wear your glasses on top of your head when not using them as this will always widen up the frames and/or put them way out of adjustment. There are a huge number of variations of plastic to choose from, so I'll just list a few of the most popular plastic materials for you here:
- Zyl aka Cellulose Acetate: Zyl is likely the most popular plastic for plastic frames to contain. It is easily adjusted, often without heat needed, to wrap around the ears for a snug fit. All acetate style plastic do have a tendency to dry out over time, and with this drying out of the material, the frame will become more and more brittle which in turn makes it more prone to breakages. The actual acetate quality will determine how fast this drying out will happen, but it will happen to all acetate plastic given enough time. You will see this is happening to your acetate frame, by noticing a cloudy like white effect on your frame that you cannot clean off with any substance. With all that in mind, and with the right fit, acetate can be a very comfortable material to wear, and will not likely cause any kind of allergic reaction or sensitivity.
Mazzucchelli acetate: Mazzucchelli Acetate is made using Cottons and colored using special powders in a unique process. This material is still technically a cellulose acetate, but made from natural ingredients making it stand out from its cousin Zyl, and tends to be a more biodegradable or eco-friendly solution. This material is derived from cotton and turned into cellulose acetate, a transparent raw base for adding color. The colors are applied with organic powders and repeatedly sent through rollers for the desired thickness. It is an easily adjustable material, and can have varying degrees of weight depending on the frame design itself.- High Injection molded plastic: You will find more often sunglasses in the high injection molded plastics, but it isn't totally unheard of to use it a regular eyeglass frame as well. The high injection molded plastic will be the lightest style of plastic frame, feeling like you may not even have a frame on at all. The biggest draw back of this style of plastic is its limited adjustability. As these plastics are injected in to design molds at a very high heat, it is not possible to bend and adjust them like you could with another plastic style that contains a reinforced temple bar to facilitate adjustment behind the ears. These temples are more meant to wrap around the circumference of your skull and hold from there, unlike most usual style of glasses that will be adjusted to wrap around your ears. Therefore, a high injection mold plastic must fit and feel good right off the bat, because it will be impossible to adjust them into the perfect fit.
- Nylon or Propionate: Nylon material is still occasionally used. Nylon is strong, lightweight and flexible, but it can become brittle with age like other acetate frames. Propionate specifically is a nylon-based plastic that is strong, flexible, lightweight and hypoallergenic. Propionate is often used in sports frames because of its durability. Nylon based frames tend to be pretty adjustable if done in the correct way, but may not be the easiest of plastics to manipulate, so a good fit before any adjustments are made is always recommended.
Combination frames
We have been through some of the most popular metal and plastic materials in this post, which leaves us with one more material style for frames. 
Combination frames will have a mixture of any of the above mentioned plastic and metal materials in one frame. Most
common would be the very retro square style frames that have a plastic brow line with a metal eye wire, and may have either plastic or metal temple, depending on the particular design. These frames could have any combination of metal and plastic as mentioned above, may also feature an acetate inlay in the eye wire depending on the style. Combination frames will come in styles that have nosepads for adjustment, or may feature a plastic bridge, so these styles tend to be fairly versatile to wear.
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That pretty much sums up the main kind of materials used in the creation of frame styles. Stay tuned to the blog for the next post in our series "Choosing new glasses"! If you missed the first post in this series you can find it HERE!
