Each widget is a subclass of their respective django.forms.widgets classes (e.g., materialdjango.PaperTextInput is subclassed from django.forms.widgets.TextInput). For more information, see Django's widgets documentation.
Note
While the following widgets are prefixed with Paper, they actually use <iron-input> styling for the moment, as <paper-input> styling doesn't work properly with <form> tags. This will be fixed eventually, and these will likely be renamed with Iron prefixes.