PHP Form Builder's Material Forms can be built with Bootstrap 4 or Materialize framework.
Bootstrap Material Forms
- Bootstrap 4 is the framework used as the main css on your page
- Material Design is a customized version of Materialize framework containing only the minimal css/js required for forms.
- These forms are using PHP Form Builder's materialize plugin
Pure Material Forms
- Materialize is the framework used as the main css on your page
- These forms don't use any extra plugin
Detailed explanations here: Material Design Forms