Cellulose acetate is derived from cotton fibres and wood pulp, making it one of the few eyewear materials with a natural, plant-based origin. First adopted for eyewear frames in the late 1940s as a safer alternative to flammable celluloid, acetate became the standard for premium eyewear and has remained so for over seven decades.

What makes acetate distinctive is its manufacturing process. Unlike injection-moulded plastics, acetate sheets are produced in large blocks and then cut, shaped, and hand-finished over multiple days. This allows for deep, layered colour combinations and tortoiseshell patterns that run all the way through the material. Acetate also adapts slightly to body temperature over time, and can be adjusted by an optician using gentle heat.

Cellulose propionate is a thermoplastic material made by combining cellulose with propionic acid. In its raw form it appears as small transparent beads that are heated, fused, and injection-moulded into frame shapes, usually with hinges and reinforcements pre-placed in the mould for added structural strength. The result is a frame that is harder, more stable, and lighter than cellulose acetate.

CP sits at an excellent intersection of properties: up to 30% lighter than acetate in equivalent thin-frame designs, harder and more warp-resistant, and it ages more slowly with better colour retention over time. The American Academy of Ophthalmology classifies CP as a hypoallergenic material, noting its lightweight properties and suitability for people with sensitive skin.

The key structural difference from acetate is that CP's colour is applied as a surface dye after the frame is shaped and lacquered, rather than running through the material. This means CP cannot replicate the deep, layered colour patterns of hand-cut acetate, but it achieves a wide range of solid colours, glossy finishes, and transparent effects. The lacquer also contributes to the smooth, polished surface feel CP frames are known for.

CP is notably more stable than acetate in warmer conditions. Its higher stiffness and lower plasticizer migration mean frames hold their shape longer and resist the colour fading and material creep that acetate can develop over years of use.

Metal frames have been a staple of eyewear since the 19th century. Modern sunglasses use stainless steel (strong, corrosion-resistant), monel (a nickel-copper alloy, highly formable), or titanium (lightest metal, biocompatible, corrosion-proof). The defining characteristic of metal is its ability to be made extremely thin, which is why aviators have stayed culturally relevant for decades. Metal frames are also adjustable at the nose bridge and temples for a precise fit.

In India's climate, corrosion from sweat and humidity is the primary concern. Quality stainless steel handles this well. Lower-grade alloys in budget frames can show oxidation and skin discolouration over time. Plated finishes wear at high-contact points after months of regular use.

TR90 is a high-performance thermoplastic polyamide developed using Swiss engineering technology, originally for industrial and military applications. At 13 to 20 grams, it is the lightest frame material in this comparison. TR90 also exhibits elastic memory: frames can be bent, twisted, or compressed and return to their original shape without permanent deformation. It is heat-resistant up to 120 degrees Celsius, hypoallergenic, and highly resistant to sweat and chemicals.

The trade-off is aesthetic. Because TR90 is injection-moulded, the colour range is more limited and the finish tends toward matte. TR90 is the right material for sports, active use, and anyone who puts their frames through physical stress daily.