Touch targets are the parts of the screen that respond to user input. They extend beyond the visual bounds of an element. For example, an icon may appear to be 24 x 24 dp, but the padding surrounding it comprises the full 48 x 48 dp touch target.
This is visible on samples like: Polymer shop in mobile view, where there is a cart icon on the right top.
Default size of paper icon button is 40x40 while from: https://material.io/guidelines/usability/accessibility.html#accessibility-style:
This is visible on samples like: Polymer shop in mobile view, where there is a cart icon on the right top.