Set the cache for static files either in web.config or via UI in IIS, for the static file folder you want to cache, add this in the config file and it works.
<configuration>
<system.webServer>
<staticContent>
<clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="1000.00:00:00" />
</staticContent>
<httpProtocol>
<customHeaders>
<add name="Cache-Control" value="public" />
</customHeaders>
</httpProtocol>
</system.webServer>
</configuration>