Short answer: light-colored wood or a quality wood-plastic composite. If I had to pick one material for a street bench in full summer sun, I’d choose thermally modified ash or white oak in a slatted design. For a cool outdoor bench that needs almost no upkeep, go with a wood-plastic composite in a light color.
The main thing to avoid is solid metal—especially steel or dark painted aluminum. Metal conducts heat extremely well, so it can get painfully hot fast. Perforated or slatted aluminum with a light powder coat is better, but it’s still not as comfortable as wood.
Solid hardwood like white oak, black locust, or thermally modified ash stays much cooler because wood has low thermal conductivity. A lighter color helps reflect heat, and gaps between slats allow airflow. Teak and ipe are durable, but darker tropical hardwoods can still warm up more than you’d expect.
If maintenance is a concern, a wood-plastic composite or recycled plastic lumber is probably the best street bench material for hot climates. These boards don’t splinter, won’t rot, and stay far cooler than steel. Avoid dark charcoal or black boards; choose sand, gray, or white-washed tones.
So my recommendation: light-colored slatted wood or wood-plastic composite bench. Place it in partial shade if possible. That setup gives you a heat-resistant bench material option that won’t turn into a frying pan in July.