# Top/Bottom Layers

Top and bottom layers define the external surfaces of 3D-printed parts, influencing aesthetics, structural integrity, and functionality. These fully dense layers bridge over infill and provide a foundation for subsequent layers. Proper configuration minimizes defects like pillowing, ensures dimensional accuracy, and enhances surface finish.

## Top/Bottom Thickness Fundamentals

### **Thickness Calculation**

* **Layer Height Dependency**: Thickness is a **multiple of layer height**. For example, a 0.2mm layer height requires **5 layers** to achieve 1mm thickness.
* **Minimum Recommendations**:
  * **Top Layers**: **1mm minimum** (e.g., 5 layers at 0.2mm) to prevent pillowing (dimpled surfaces caused by sagging over sparse infill).
  * **Bottom Layers**: **0.6mm minimum** (e.g., 3 layers at 0.2mm) for adhesion and stability.

### **Adjustments for Infill Density**

* **Low Infill (≤15%)**: Increase top layers (e.g., 6–8 layers) to compensate for reduced support depending on part geometry.
* **High Infill (≥30%)**: Fewer top layers (e.g., 4–5 layers) suffice due to dense underlying structure.

**Note**: Round thickness to the nearest layer height increment (e.g., 0.9mm for 0.3mm layers instead of 0.8mm).

## Advanced Top/Bottom Layer Settings

### **Monotonic Order**

* **Function**: Forces lines to print in a single direction (e.g., left-to-right) for uniform overlap, eliminating inconsistent surface textures.
* **Benefits**: Reduces bulges and improves flat surface quality.
* **Drawbacks**: Slightly increases print time

 The image below shows a print on the left without checking Monotonic Top/Bottom Order, and the right is with it checked on.

<figure><img src="https://3491278982-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCp7LK0pgIUpVwJdO2wqk%2Fuploads%2FE2sdaI0bfn02uH37C7lA%2Fmono.jpg?alt=media&#x26;token=0357519f-a3d8-43f5-9738-32cff2cbc54b" alt=""><figcaption><p>Monotonic Top Layers on Right</p></figcaption></figure>

### **Ironing**

* **Process**: The nozzle reheats and smooths the top layer without extruding filament.
* **Applications**: Ideal for flat surfaces (e.g., tabletops, enclosures) requiring a polished finish.
* **Limitations**: Ineffective on curved surfaces; requires precise calibration of **ironing speed**, **flow rate**, and **temperature**.

<figure><img src="https://3491278982-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FCp7LK0pgIUpVwJdO2wqk%2Fuploads%2FFRbOmFqixXzuEbDkfrku%2Ftops.jpg?alt=media&#x26;token=ff8298a3-bc51-49fa-a196-d6d4daf05df8" alt=""><figcaption><p>Left is a standard print, right is with ironing on</p></figcaption></figure>

### **Line Directions**

* **Impact**: Aligning top/bottom lines with part geometry (e.g., 45°/-45° crosshatch) reduces visible seams and improves strength.
* **Optimization**: Adjust angles to minimize bridging gaps or align with load-bearing axes.

## Troubleshooting Common Issues

### **Pillowing (Dimpled Top Surfaces)**

* **Causes**: Insufficient top layers, low infill density, or excessive cooling.
* **Solutions**:
  * Increase top layers to **1.2–1.5mm**.
  * Raise infill density to **20–30%** for better bridging support.
  * Reduce part-cooling fan speed for slower solidification.

### **Warped Bottom Layers**

* **Causes**: Poor bed adhesion, uneven heating, or insufficient bottom layers.
* **Solutions**:
  * Increase bottom layers to **0.8–1.0mm**.
  * Use adhesives (e.g., glue stick, Magigoo, PEI sheets) and ensure bed leveling.

### **Ironing Artifacts**

* **Over-Melting**: Lower ironing temperature or reduce flow rate.
* **Incomplete Smoothing**: Increase ironing passes or slow movement speed.

## Practical Workflow for Configuration

1. **Assess Model Requirements**:
   * **Flat Surfaces**: Prioritize monotonic order and ironing.
   * **Curved Surfaces**: Disable ironing; focus on layer thickness.
2. **Calibrate Settings**:
   * **Top Layers**: Start at **1mm** (5 layers at 0.2mm); adjust based on infill density.
   * **Bottom Layers**: Use **0.6–0.8mm** (3–4 layers at 0.2mm) for adhesion.
3. **Validate with Test Prints**:
   * Print calibration squares to check for pillowing or warping.
   * Test ironing on flat benchmarks (e.g., XYZ cubes).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://wiki.polymaker.com/the-basics/3d-slicers/top-bottom-layers.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.