Those comfortable cushions you see on modern urban benches are typically attached through several practical methods that balance security with maintenance needs. Most public benches use either industrial-grade hook-and-loop fasteners (heavy-duty Velcro) along the bottom of cushions, which creates a strong bond while allowing for easy removal when cleaning or replacement is needed. Alternatively, many designs incorporate strategic snapping systems where durable plastic or metal snaps connect cushion covers directly to the bench frame. Some higher-end designs even feature zippered connections that wrap around structural elements.
Regarding waterproof capabilities, this varies significantly by municipality and design purpose. While the cushion filling itself is rarely waterproof (typically being high-density foam), the outer fabric makes all the difference. Many urban benches use solution-dyed acrylic fabrics that are inherently water-resistant and quick-drying. These specialized textiles prevent water absorption while resisting mildew and UV damage. However, it's important to understand that "water-resistant" doesn't mean completely waterproof - during heavy rainfall, water can still penetrate through stitching holes or zipper areas.
The attachment methods themselves contribute to water management too. Snapped and zippered designs generally provide better protection against water seeping underneath compared to hook-and-loop systems. Many cities opt for quick-dry cushions with drainage holes in the bench frames beneath them, allowing water to escape rather than pool. So while you can't expect urban bench cushions to withstand a torrential downpour completely dry, quality designs do incorporate smart attachment systems and weather-resistant materials to handle typical urban weather conditions while maintaining both comfort and durability for public use.