If you are shopping for an outdoor bench that will live in a desert climate with extreme heat, the single most important thing to know is this: there is no perfect material, but there are two clear winners for real-world comfort and durability. Powder-coated aluminum frames with HDPE (high-density polyethylene) lumber slats are usually the best overall choice. A close second is heat-treated wood, often sold as thermally modified ash or pine. Let me explain why, and also tell you which materials you should avoid unless you enjoy third-degree burns on the back of your thighs.
The biggest problem in a desert is not just air temperature. It is surface temperature. A metal bench sitting in direct 110°F sun can easily reach 160°F to 180°F. Uncoated steel or raw aluminum will burn you instantly. That is why any bare metal is a terrible idea. Powder coating helps a lot, but even powder-coated aluminum can get uncomfortably hot if it is a dark color. The real trick is to combine a metal frame that stays structurally stable with slats made from a material that does not conduct heat aggressively. HDPE lumber does exactly that. It is made from recycled plastic, it does not splinter or rot, it resists UV damage extremely well, and it stays significantly cooler to the touch than metal because plastic is a poor thermal conductor. It also does not absorb moisture, so desert monsoon flash rains will not cause swelling or cracking. The only minor downside is that very cheap HDPE can become slightly soft at temperatures above 130°F, so choose a reputable brand with a high-density formulation.
Heat-treated wood is the other excellent option. The thermal modification process cooks the wood at over 400°F in a low-oxygen environment. This changes the cell structure so the wood becomes much less attractive to moisture, much more dimensionally stable, and naturally darker in color without any stain. In a desert, that stability means the boards will not cup, warp, or shrink as dramatically as untreated wood during the massive day-to-night temperature swings. It still feels like wood, so it stays cooler than metal and looks beautiful. You will need to apply a UV-protecting oil once or twice a year if you want to keep the rich color from fading to a silvery gray, but the bench will last for decades. Avoid untreated softwoods like pine or cedar. They will dry out, crack, and splinter within a couple of seasons in extreme aridity.
What about concrete or stone benches? They are incredibly durable and will never blow away in a sandstorm, but they absorb heat all day and release it slowly at night. In the late afternoon, a concrete bench can be hotter than a car hood. They also feel harsh and cold during the brief desert winter nights. If you love the look, place them in full shade or add thick cushions. Solid teak is often marketed as premium outdoor furniture, but natural teak is not ideal for extreme desert dryness. It can develop deep cracks as it loses its internal oils rapidly. Thermally modified teak would work, but it is very expensive for what you get.
One more material worth mentioning is powder-coated steel. It is stronger than aluminum and often cheaper, but it will eventually rust if the coating gets scratched, and it holds heat longer than aluminum. If you choose steel, make sure it is hot-dip galvanized before powder coating, and check the coating for chips every spring. For most people, the best practical bench for a desert patio, garden, or trailhead is a simple design with a powder-coated aluminum frame, light-colored HDPE slats, and stainless steel hardware. It will stay cooler, resist UV fading, handle sand and dust without jamming, and require almost zero maintenance for 15 to 20 years. If you prefer the warmth of natural wood, choose thermally modified ash or pine and commit to a light annual oiling. Either way, skip the bare metal, skip the cheap softwood, and you will actually enjoy sitting outside even when the thermometer reads 115.