A 12" / 30 cm reusable piping bag.
These bags are an excellent quality, ours last for years & they get lots of use!
They can be used with just a piping tip popped inside but using them with Wilton standard couplers stops icing from squeezing out the sides & make it much easier when you need to change tips.
Tip! Wash them with warm soapy water & dry over taps or form into a "teepee".