Ann: VHD Technology - Thermal Performance Breakthrough, page-78

Really, I think Clinton’s time is too valuable to be physics teacher to investors. the answer is plain if one carefully studies the information GCM already released.

Maybe this helps.
In conductive materials like metals, heats travels from hot to cold, in all directions. If the conductive body has corners, like a copper rod with bent at 90 degrees , the corner does not stop the heat passing through.
VHD graphite has a high degree of anisotropy which means that properties depend on the direction in which they are measured.

Imagine a material built up like a pancake of very thin layers of metal separated by a thin films of mica. (Mica is a mineral which is an electrical as well as a thermal insulator)

Such pancake material would conduct heat preferentially along the layers (grain).
VHD graphite blocks conduct heat in much the same way. (Thermal Conductivity, 20°C (//): 617 W/m.K Thermal Conductivity, 20°C (┴): 11 W/m.K), which means that the conductivity across the grain is about 2% of the conductivity along the grain.

Along the grain the heat flows from hot to cold quite fast (617 W/m.K) it flows freely in any direction parallel with the grain
Across the grain the heat also flows in any direction perpendicular to the grain, but very, very slowly, (11 W/m.K)