Material design: Progress & activity
<paper-progress indeterminate class="blue"></paper-progress>
<paper-progress indeterminate class="slow red"></paper-progress>
<paper-progress value="40" secondary-progress="80"></paper-progress>The progress bars are for situations where the percentage completed can be determined. They give users a quick sense of how much longer an operation will take.
There is also a secondary progress which is useful for displaying intermediate progress, such as the buffer level during a streaming playback progress bar.