We're not really sure what to call them.  

They're far too thin to be called "heatsinks" with a straight face.  Certainly they aren't a real heatsink, so please assume they will do very little in terms of cooling!  But they would be effective at drawing away a little bit of heat from a relatively cool-running component you don't want to run warm (we've seen people use them successfully with gainclones, YMMV).  We aren't providing a cooling rating for them - please use your discretion when deciding what you are going to do with them.

What makes these side panels really remarkable is the flexibility they offer to the DIY builder for internal (or external) mounting options.  

One side has a horizontal "C shaped mounting groove" in the middle that stretches the whole way across, and  four "U shaped" grooves.

The other side is relatively smooth, with just two "C shaped grooves" running its width.

These grooves offer a range of creative DIY uses only limited by your imagination and are a really fun complement to any chassis.

• They can be mounted inside out, giving you a choice of either a multi finned exterior with 5 visible channels or a smoother exterior with 2 channels 
   
• You could use the grooves to slide in brackets or PCBs
   
• The "C shaped grooves" accept M3 bolts and when used with a hexagonal nut (as pictured) the flat sides will stop the nut from spinning, giving you a great way to bolt things to the sides of your case
   
• Fillister Head Slotted Machine Screws with a 6-32 thread also nicely slide into the "C shaped" grooves (but will spin)