Titanium: depending how it’s used, either weight savings or a premium aesthetic look.
Copper: heat dissipation and/or aesthetic look, either for patina or shine.
Copper can be hand polished, dip it in ketchup will remove a lot of the tarnish. I consider the patina to be a selling point on a copper light. Brass will patina as well, but not to the extent a copper light will.
Patina is a artsy term for oxidization. It is created by a reaction to air/water/skin oils and causes the surface to darken and shade. Look at a true copper penny, this is patina!
Patina can be encouraged by exposure to things like eggs gassing out, chemical application and other methods. It can be brown, green, blue and other colors depending upon what created the patina.
I for one like natural patina or darkening. You will end up with finger prints, recessed areas will not be as dark and areas that are rubbed regularly will take on a different shade as well.
Another lesser known but very important benefit of copper is its effective anti-microbial properties. It would be useful if you use your flashlights while working in sanitation facilities.
I think the “exotic materials are pretty much all about aesthetics and having something different.
From a practical perspective, I conclude that aluminum is by far the best material for modern LED flashlights.
Aluminum - Pros: very lightweight, good thermal properties (good conductivity and when dark-anodized excellent emissivity), threads work well, can be anodized. Low-cost. Cons: bare aluminum scratches easily. Anodizing can wear off… especially common with cheaper Type II anodizing. Silvery scratches are quite visible against dark-colored anodizing. Polished bare aluminum does not have good thermal emissivity.
Titanium - Pros: lightest weight of the exotic materials found in commonly available flashlights. Looks stylish when polished. Much more durable than bare aluminum. Can be anodized or PVD coated. Cons: considerably heavier than aluminum, worse thermal properties, Ti on Ti tends to produce gritty threads.
Copper - Pros: looks gorgeous without patina. Some may like the darker patina. Bare copper self-cleans itself of germs via the oligodynamic effect. Excellent heat transfer. Cons: Very heavy. Polished copper has low emissivity compared to dark anodized aluminum (it doesn’t radiate heat well). Heat conductivity may be a bit too good if it means there is no portion of the light cool enough to hold on to. Not very durable if dropped.
Brass - Pros: looks similar to copper. Doesn’t dramatically develop a dark patina like pure copper. Cons: Very heavy. Thermal transfer is not as good as copper or aluminum.
Stainless Steel - Pros: looks stylish. Extremely strong and durable. Cons: tremendously heavy. Very poor thermal properties.
From a practical perspective, Aluminum wins hands down. It’s just a better material to build a practical flashlight out of. The biggest downside of aluminum is it doesn’t wear well and may not feel special since most lights are aluminum.
Most people aren’t flashaholics like us and regard their flashlights as tools. They don’t care if their flashlight looks scuffed so long as it still works fine. The ultimate purpose of a flashlight is to produce light.
I have titanium and copper lights, and I sometimes EDC them. But sometimes it feels a bit awkward grabbing a light for EDC that is 70% heavier than the aluminum version sitting on the shelf next to it, just so I can have something that looks prettier when not in operation.
Durability counts for a lot when you are relying on a light. Things feel more secure when using a Ti/Cu light than when using aluminum (think coke can, LOL). So aluminum around the house and town, but Ti/Cu on the trail or at least aluminum with a stainless steel bezel. But that is just me, you can always take some extra flashlights.
When I was in the Marines (and still smoked) I had a brass zippo I carried for years. The natural patina on it kind of told its own story. I think I even had a stain on it from a few drops of blood.
After a while, they turn brownish and can almost pass for wood.
Dunno. I never got it. I’d prefer that nice deep salmon-pink of pure clean shiny Cu, which only lasts when coated. One little chip in the coating, and you don’t just recoat the chip, but essentially gotta strip it down completely, repolish it, and recoat it.