Add .active to .progress-bar-striped to animate the stripes right to left. Not available in IE9 and below.

45% Complete
<div class="progress">
  <div class="progress-bar progress-bar-striped active" role="progressbar" aria-valuenow="45" aria-valuemin="0" aria-valuemax="100" style="width: 45%">
    <span class="sr-only">45% Complete</span>
  </div>
</div>

Related classes: