node_modules/material-design-lite/src/textfield/snippets/textfield-multi-line.html

<!-- Floating Multiline Textfield -->
<form action="#">
  <div class="mdl-textfield mdl-js-textfield">
    <textarea class="mdl-textfield__input" type="text" rows= "3" id="sample5" ></textarea>
    <label class="mdl-textfield__label" for="sample5">Text lines...</label>
  </div>
</form>