_modal.html.erb

<form action="{{ folderPath(openFolder) }}" method="post" class="folder_form" enctype="multipart/form-data">
...
<fieldset>
  <label for="folder_blablabla">Blablabla {{openFolder.blablabla}} </label>
  <input type="text" name="folder[blablabla]" id="folder_blablabla" data-ng-model="openFolder.blablabla" />
</fieldset>
...
</form>

folder.rb

# model/folder.rb
...
field :blablabla, type: String
...