The straw spout is made from food grade silicon. It is a soft mouthpiece that has a 5mm diameter opening that allows for thinner type foods like purees. 

Its a great option for younger children. It will slow down the speed that the food is dispensed and it will stop kids from putting their finger inside the spout due to its smaller opening. 

It can easily be interchanged with the spout that comes with the Subo which is 12mm.