Updating Webpage from Within Thread

I have a webpage that runs a lengthy procedure, it's all working apart from displaying the progress on the page.

I have the following progress bar (Bootstrap):

<div class="col-md-8">
  <label for="product-feed-progress">Progress</label>
    <div class="progress">
     <div class="progress-bar" role="progressbar" runat="server" id="prgProdFeed" style="min-width: 0em; width: 0%;">
                                    0%
     </div>
  </div>
</div>

During the thread, I have the following snippet that adjusts the width property of prgProdFeed:

prgProdFeed.Attributes.Add("style", "width:" & ((p_objFeedInfo.Progress / p_objFeedInfo.Total) * 100).ToString() + "%")

I have also tried:

prgProdFeed.Style.Item("width") = ((p_objFeedInfo.Progress / p_objFeedInfo.Total) * 100).ToString() + "%"

They both change the width property of the bar which currently sits in an update panel (updated on the tick of a timer).

How come my progress bar is not updating on the page? I can see using the inspector that the update panel is refreshing, and in the debugger it's showing the width being correct - just nothing changes visually.

Any help would be appreciated.