Not necessarily. Any outdoor cushion can work if it is genuinely outdoor-rated and fits your furniture properly. The cushion should use solution-dyed or UV-resistant fabric, quick-dry foam, and a mildew-resistant cover. It also needs a removable cover for cleaning, because city balconies and roof decks collect dust, pollen, and pollution.
Urban settings do add a few practical demands. Space is usually tight, so outdoor cushion fit matters more than on a big suburban patio. Measure the seat depth, width, and back height before buying; a standard cushion that is too deep can push you forward or block a folding chair. Look for slim profiles, corner ties, or non-slip bases if your urban outdoor furniture is lightweight or exposed to wind. If your chairs are modular, metal, or built for small balconies, you may need custom or made-to-measure cushions rather than a generic size.
Weather and storage are the other issues. Even on a covered city balcony, rain can blow in, and sun can fade fabric fast. Choose weather-resistant outdoor cushions with drainage, quick-dry foam, and mildew-resistant outdoor cushions that can handle damp air. If you have no storage, pick cushions with removable, washable covers and bring them inside during heavy rain. So the short answer is: you do not need “special” cushions in a luxury sense, but you do need true outdoor cushions with the right fit, weather resistance, and security for urban use. Generic indoor cushions or cheap outdoor-look cushions usually won’t last.