When piping roses on cupcakes, a closed star piping nozzle is typically used to achieve the desired rose shape. The most commonly recommended nozzles for piping roses are Wilton 1M and Wilton 2D. These nozzles have a star-shaped opening with multiple points, allowing you to create beautiful, textured petals that resemble rose blossoms. The Wilton 1M nozzle is slightly larger and produces larger roses, while the Wilton 2D nozzle creates slightly smaller roses with more defined petals. Both nozzles are popular choices among bakers and decorators for piping roses on cupcakes due to their versatility and ability to create stunning floral designs. It's worth noting that while these two nozzles are commonly used for rose piping, you can experiment with other closed star nozzles as well. Different brands may have their own numbering systems for piping nozzles, so look for a similar star-shaped nozzle with multiple points to achieve the desired rose effect. Ultimately, the choice of nozzle depends on personal preference and the size of roses you wish to pipe. It's recommended to try different nozzles and practice piping roses on a parchment paper before moving on to the cupcakes, allowing you to determine which nozzle works best for your desired design and aesthetic.