NOTE: This block was removed in Refined Storage 1.7. The landscape for covers and multiparts in Minecraft 1.14.4 is a bit unclear, so time will tell if this feature returns, or if Refined Storage will utilise a multipart library if that is available.
A Cover is an item used to hide cables.
It will block network connections, cables can't pass through the "hidden" side.
You can craft a Cover with a Cutting Tool and the block of your choice to use for hiding.