I’d start by blocking the heat before it builds up. If you can, move seating under a pergola, shade sail, umbrella, or even a deciduous tree—morning shade is nice, but late-afternoon shade is what really saves a west-facing bench. Choose light-colored, breathable materials like slatted wood, aluminum, or woven resin rather than dark metal or solid plastic; dark surfaces soak up sun and hold heat. If you already own dark furniture, a fitted cover or light-colored throw can help, but take it off when the furniture is in direct sun so heat doesn’t get trapped.
For cushions, go for quick-dry, breathable fabrics and keep them out of the sun when not in use. A damp towel or a light spray of water can cool a hot seat quickly, but don’t soak metal or wood repeatedly. In very hot cities, I keep a small spray bottle and a folded cotton throw nearby—it sounds fussy, but it makes a metal chair usable in minutes. Also, position furniture so air can move underneath; slatted or mesh seats stay cooler than solid ones. If you have a hose, a brief mist of the surrounding paving and furniture legs in the late afternoon helps lower surface temperature, but avoid water on electronics and check for slipping hazards.
Practical extras: set up a temporary shade sail in peak afternoon, add a tray of cold drinks on a shaded side table, and rotate seating to the cooler side of the building. If you’re buying new pieces, test the surface in direct sun and favor designs with airflow, light finishes, and removable cushions. Finally, use the furniture earlier in the day or after sunset. In a city, shade, airflow, and surface color do most of the work—fancy cooling gadgets are usually optional.