The key difference between Prepreg and Core is their state of resin curing and primary function: Core is a fully cured, rigid structural substrate clad with copper, while Prepreg is a flexible, partially cured material used as an adhesive to bind layers together during lamination.

Direct Comparison

Feature	Core Material	Prepreg (Pre-impregnated)
Resin State	C-stage (Fully cured): Solid, rigid, and thermally stable.	B-stage (Partially cured): Soft, pliable resin that melts under heat and pressure.
Copper Cladding	Comes pre-laminated with copper foil on one or both sides.	Comes without copper (pure fiberglass weave soaked in resin).
Primary Function	Provides main mechanical rigidity and internal base layers.	Acts as glue/insulation to bond Cores and outer copper foils.
Rigidity	Stiff and rigid prior to lamination.	Flexible and pliable until heat-cured during lamination.
Thickness Control	Fixed, precise factory thickness.	Thickness compresses slightly when melted under press.

How They Work Together in Manufacturing

1. Inner signal circuits are etched directly onto a Core.

2. Layers of Prepreg are sandwiched between the etched Cores and outer copper foils.

3. The entire stackup is placed in a heated hydraulic press. The heat melts the Prepreg resin, filling gaps between copper traces.

4. Once cooled, the Prepreg cures completely (moving from B-stage to C-stage), forming a single, solid multi-layer PCB.