The back of the CB sheet is coated with micro-encapsulated dye or ink. When pressure is applied (e.g., writing or printing), the dye capsules rupture, transferring the image to the sheet below.
The CF sheet has clay on its front surface, which reacts with the dye from the CB or CFB above to create a permanent mark. It is typically the bottommost sheet in a set.
CB transfers information downward via its coated back. CF receives information via its clay-coated front. They are not interchangeable because CB cannot react with itself—it requires CF's clay coating for image transfer. Similarly, CF cannot transfer information upward without a CB or CFB layer above it