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In NCR paper sets (No Carbon Required), the difference between top sheets and bottom sheets lies in their coating and function within the multi-part form. NCR paper is designed to create instant, chemical-based copies without using carbon sheets. This is achieved by applying micro-encapsulated dye and reactive coatings to the paper, enabling handwritten or printed impressions to transfer from the top layer through to the subsequent layers below.
Let’s break down the key differences between top sheets, middle sheets (if any), and bottom sheets:
1. Top Sheet (CB – Coated Back)
Definition: The top sheet in an NCR set is called the CB (Coated Back) sheet.
Function: It’s the original writing surface. When you apply pressure to this sheet (by writing or printing), it activates the dye capsules on the underside of the page.
Coating: Only the back side of the sheet is coated with micro-encapsulated dye, also known as color developer ink.
Purpose: Transfers written or printed content to the sheet below it.
Position in the Set: Always the first (top) page in the NCR form.
2. Middle Sheet(s) (CFB – Coated Front and Back)
Definition: Middle sheets in multi-part forms are called CFB (Coated Front and Back).
Function: These sheets receive the image from the sheet above and transfer it to the sheet below.
Coating: Coated on both sides:
The front side has a clay-based reactive coating.
The back side has dye microcapsules.
Use Case: Common in 3-part or more NCR sets (e.g., invoice books with copies for customer, office, and accounting).
3. Bottom Sheet (CF – Coated Front)
Definition: The bottom sheet is known as the CF (Coated Front) sheet.
Function: This is the final sheet in the set and is designed to receive the transferred image, but not to transfer it any further.
Coating: Only the front side (the top of the sheet) is coated with a reactive clay material.
Purpose: Reacts with the dye released from the sheet above to create a visible copy.
Position in the Set: Always the last page in the NCR form.
Summary Table of Differences
| Sheet Type | Position in Set | Coated Side(s) | Function |
| CB (Top Sheet) | First | Back side only | Transfers writing to the sheet below |
| CFB (Middle) | Middle (if needed) | Both front and back | Receives and transfers writing |
| CF (Bottom) | Last | Front side only | Only receives writing |
Why This Matters
Understanding the role of each sheet in an NCR set is essential for:
Custom printing (applying graphics, terms, logos correctly).
Assembling multi-part forms with the right coating sequence.
Ensuring clear copy quality from the top to the bottom page.
