At first I intended to modify the cup lid that I already had, with the implementation of a bar that a plugging mechanism could rotate around. Overall, I decided to deviate from this idea, as the center of the original lid did not dip low enough and I thought it would be pretty complicated to implement. I opted for making a new lid, where instead of a rod that could rotate down and plug up the hole for supping, the user could rotate a flat piece of acrylic over the hole. I also chose this because I thought it would require me to only bend one piece of acrylic and I do not have a lot of experience with using heat guns. Some photos of my prototyping process are shown below.  I made the most modifications to the piece that I heat formed from flat to curved, as I didn't want the ends to meet at the end (to allow room for the user's mouth when sipping out of the cup), and also wanted a thinner piece.