How many seconds a heatmap image can be cached on the client's browser. This is a per-client setting and does not always force a heatmap image to be cached. Typically, a user's browser will cache the images it downloads for a short period and will not re-download the image unless the user forces the browser to reload all images. If left blank, no expires header is sent to the client.

This setting will help reduce load on your web server. <b>Only works on Apache web servers!</b>

<b>Recommendation:</b> 1 hour (3600 seconds)