Google's material design champions the use of text fields that imitate ruled lines on a piece of paper. This is a pattern that seems acceptable to me when using a mouse because of the precision that the mouse allows.
My concern is that when on a touch device the user feels much more comfortable targeting a bounded box, and that text alone or lines offer much less affordance than an object to press.
Has anyone encountered usability issues on touch devices while implementing these material design forms? Noticed any discrepancy in conversions or difficulty inputing information?