What factor primarily influences the adhesion of a layer to another in FDM printing?

The temperature of the print bed plays a crucial role in the adhesion of layers during Fused Deposition Modeling (FDM) printing. When the print bed is heated to the appropriate temperature, it helps in maintaining the warmth of the extruded filament as it is deposited. This warmth ensures that the layers of filament adhere well to each other, minimizing the risk of warping and promoting better layer bonding as the material cools down uniformly.

An optimal print bed temperature helps to create a stronger bond between the polymer chains of the filament, allowing for a more reliable structural integrity of the completed print. If the bed is too cold, the lower temperatures can lead to poor adhesion, resulting in issues such as layer separation or warping.

The other factors mentioned, such as filament color, extruder speed, and the type of cooling system, can influence aspects of the printing process but are not primarily responsible for layer adhesion. Filament color does not significantly affect adhesion; extruder speed can influence how well the material is laid down but does not directly affect the bond between layers; and while a cooling system impacts how quickly layers solidify, it is specifically the print bed temperature that is critical for ensuring strong layer adhesion.