What sort of technology does the TSA use?

Because you know what my laptop case is made of?  Fabric, probably polyester or something, and foam.  

Know what the back of my messenger bag is made of?  Fabric, probably polyester or something, and foam.  

What sort of magic x-ray machines does the TSA use that can somehow see through the (in fact, denser) fabric of my messenger bag, but I'd need to by a special laptop case for them to be able to see through that?  

(This security checkpoint brought to you by Targus and Skooba)