Layer Adhesion Strength Calculator
Scores the expected inter-layer bond strength for FDM prints based on nozzle temperature, bed temperature, layer height, print speed, and material. Use it to tune settings before printing structural parts.
About this calculator
Layer adhesion in FDM printing is determined by how well molten filament bonds to the layer below before it cools. Four key parameters govern this: nozzle temperature, bed temperature (especially for the first layer), layer height, and print speed. The scoring formula used here is: Score = ((nozzleTemp − 180) / 50 + (bedTemp / 80) + (0.3 / layerHeight) + (80 / printSpeed)) × materialType × 25. Higher nozzle temperatures keep the filament more fluid for longer, improving fusion. Higher bed temperatures reduce thermal stress in lower layers. Thinner layer heights increase the contact area between adjacent layers relative to their volume. Slower print speeds give the hot filament more time to flow and bond. The materialType coefficient adjusts the score for the intrinsic bonding properties of each filament (e.g., PETG bonds differently than PLA). The ×25 scale converts the dimensionless sum into a readable 0–100+ adhesion index.
How to use
For PLA (materialType = 1.0), nozzleTemp = 210°C, bedTemp = 60°C, layerHeight = 0.2 mm, printSpeed = 50 mm/s: Score = ((210−180)/50 + (60/80) + (0.3/0.2) + (80/50)) × 1.0 × 25 = (0.6 + 0.75 + 1.5 + 1.6) × 25 = 4.45 × 25 = 111.25. Raising nozzle temp to 220°C adds (10/50)=0.2 to the bracket, pushing the score to (4.65)×25 = 116.25 — a ~4.5% improvement in the adhesion index.
Frequently asked questions
What nozzle temperature gives the best layer adhesion for PLA?
For PLA, nozzle temperatures between 205°C and 220°C typically produce the strongest layer bonds. Below 200°C, the filament may not fully melt between layers, creating weak, brittle interfaces. Above 230°C, PLA can degrade, string excessively, and lose dimensional accuracy. The optimal point varies by brand and color (darker pigments sometimes require slightly higher temps), so printing a temperature tower — a single print that spans a range of temperatures — is the most reliable way to find your filament's sweet spot before committing to a structural print.
How does print speed affect layer adhesion in FDM 3D printing?
Faster print speeds give the deposited bead less time to transfer heat into the layer below before the nozzle moves away, resulting in weaker inter-layer bonding. This is why perimeter (outer wall) speeds are usually set 30–50% lower than infill speeds in most slicer profiles — perimeters are structural and cosmetic, while infill just needs to fill space quickly. For functional parts requiring maximum strength, printing at 30–40 mm/s rather than 60+ mm/s can meaningfully improve tensile strength perpendicular to the layer direction. The relationship is not linear: halving the speed does not double the bond strength, but the improvement is measurable.
Why does layer height influence the strength of 3D printed parts?
Thinner layers create more layer interfaces per unit of height, but each interface has a larger contact-area-to-volume ratio, meaning more of the material is actively bonded to adjacent layers. This generally improves tensile and shear strength perpendicular to the build direction. However, very thin layers (below 0.1 mm) can paradoxically weaken parts if the nozzle does not have enough clearance to deposit a proper bead, causing under-extrusion. The classic guideline is to keep layer height between 25% and 75% of the nozzle diameter — so a 0.4 mm nozzle works best with 0.1–0.3 mm layers.