The short answer is yes—metal on street benches can get slippery when it rains, but not all metal benches are the same. Some become dangerously slick, while others stay relatively grippy because of how they are made.
Rain alone can make any smooth surface slippery, but metal is especially prone to it. Water forms a thin layer between the metal and whatever touches it, reducing friction. Add in city grime, oils, pollen, and worn paint, and that layer becomes even more slippery. Polished or glossy metal is the worst because there are no micro-grooves to channel water away.
If the bench has a powder-coated finish, a brushed surface, or a textured anti-slip pattern, it is far less slippery. Many modern street benches are made from anodized aluminum or galvanized steel with ribbed or perforated seats. Those ribs and holes give water a place to drain and give your hands or clothing better grip. Older smooth painted iron benches, on the other hand, can feel like ice after a shower.
Before you sit, run your fingers over the surface. If it feels slick and shiny, treat it like a wet tile floor. If it feels matte, grainy, or rough, you should be fine. Pay attention to slope and standing water too. Flat metal slats can hold a film of water, while curved or sloped slats let rain run off.
Practical tips for rainy days: look for texture, ribs, or perforations; wipe the seat with your hand or a tissue if you can; sit on a jacket, bag, or newspaper if the surface feels slick; avoid polished or repainted smooth metal after rain; and give yourself a quick test by pressing your palm flat on the seat.
So, should you worry? A little. Metal street benches can get slippery in the rain, especially if they are smooth, painted, or worn. But many outdoor benches are designed with wet weather in mind. When in doubt, check the surface before sitting. A second of caution is better than a wet, bruised afternoon.