The solid printed layers that close off the top and bottom surfaces of a model, covering the internal infill structure.
Top and bottom layers are fully solid: they bridge over and under the infill to create a closed, smooth surface. The number of solid layers determines surface quality and the minimum wall thickness at the extremities of a model. Too few top layers with low infill causes pillowing: the solid layers cannot bridge across wide infill gaps without sagging. Typical settings: 3-5 layers top, 2-4 layers bottom. Layer thickness is typically 0.2 mm, so 4 layers = 0.8 mm solid top.
Use 4-5 top layers for smooth surfaces with infill below 40%. Increase to 6-8 layers if pillowing persists. Set bottom layers to 3-4 for adequate bed separation. Enable ironing on top surfaces for a near-flat finish: the nozzle slowly re-passes the top surface with minimal extrusion to fill micro-voids. Match top/bottom layer width to perimeter width for clean edges.
Too few top layers with 15% infill almost always causes pillowing: increase either layer count or infill. Printing top layers too fast causes gaps and roughness: reduce top/bottom speed to 25-40 mm/s. Ironing causes heat-related colour change on matte filaments. Bottom layers on a textured PEI plate inherit the texture; use smooth PEI if optical-quality bottom face is needed.
Related terms: Infill, Wall / Perimeter, Print Speed
| Field | 3D printing |
|---|---|
| Also called | solid layers, skin layers |
| Source | EDi Brain: tech/fdm |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert