Understanding Print Cooling and Why It Matters

Harry S.

Hot Plastic Needs to Cool Fast

The moment molten filament leaves the nozzle, cooling becomes a race against gravity. The plastic needs to solidify quickly enough to hold its intended shape before the next layer is deposited on top of it. If cooling happens too slowly, overhangs begin sagging, bridges droop, corners soften, and small details lose definition. If cooling happens too aggressively, layers may not bond together properly, leaving prints brittle and prone to splitting. Finding the balance between those two extremes is one of the most important parts of tuning print quality in FDM printing.

Part cooling specifically refers to the fan that is directed at the active print area. This is separate from the hotend cooling fan, which runs continuously to prevent heat creep inside the extruder assembly, and separate again from any electronics cooling fans inside the printer itself. The part cooling fan is the one controlled through slicer settings, usually expressed as a percentage between 0% and 100%.

Material Specific Cooling Requirements

Different materials respond to cooling very differently, which is why fan settings that work perfectly for one filament can entirely ruin another.

PLA

PLA benefits heavily from strong cooling. Most PLA profiles run the part cooling fan at or near 100% after the first few layers. Because PLA prints at relatively low temperatures, it solidifies quickly when exposed to airflow, allowing sharper overhangs, cleaner bridges, and better detail retention.

Insufficient cooling on PLA often appears as:

• sagging overhangs
• rounded corners
• soft bridging
• blobs around fine details
• poor small feature definition

Good cooling is one of the reasons PLA is generally considered such an easy material to print successfully.

PETG

PETG is much more sensitive to excessive cooling. Unlike PLA, PETG relies on retaining more thermal energy for proper layer adhesion. Running the fan too aggressively can cool layers before they properly bond together, leading to brittle prints or visible layer separation.

Most PETG profiles work best somewhere around 40–70% fan speed depending on the printer and geometry being printed.

The ideal balance is enough airflow to control sagging and stringing without sacrificing strength between layers.

ABS and ASA

ABS and ASA prefer minimal active cooling. Rapid cooling is one of the primary causes of warping and layer splitting in these materials. As the outer surfaces cool too quickly, they contract unevenly against the hotter inner layers, creating internal stresses that pull corners upward or separate layers apart entirely.

For this reason, ABS and ASA are commonly printed with the following:

• minimal fan speed
• fully enclosed printers
• warm ambient chamber temperatures

The goal is slow, controlled cooling rather than aggressive airflow.

Fan Duct Upgrades

Many stock cooling systems on entry level printers are surprisingly inefficient. Poorly designed fan ducts often direct airflow unevenly around the nozzle, creating inconsistent cooling zones across the print. One side of the model may cool perfectly while another side remains soft and unstable.

Such conditions can produce:

• inconsistent overhang quality
• uneven surface finish
• asymmetrical bridging performance
• unpredictable detail quality

Aftermarket cooling ducts are one of the most popular functional printer upgrades because they improve airflow distribution dramatically. Try the temperature calibration process

Well known designs like the following:

• Hero Me
• BerdAir
• various dual fan systems

Focus on directing airflow evenly around the nozzle from multiple angles simultaneously. The improvement can be surprisingly noticeable. Bridges that previously sagged badly may suddenly print cleanly using the exact same temperatures and speeds simply because cooling distribution became more effective.

Temperature and cooling work together

Cooling performance should never be viewed in isolation from print temperature. A nozzle temperature that is too high is often the real reason overhangs struggle or bridging performs poorly. The plastic remains molten for too long before solidifying, making the cooling fan work far harder than necessary. This is why temperature calibration should almost always happen before major cooling modifications.

Once you properly tune the temperatures, you can evaluate cooling upgrades and fan adjustments much more accurately. Like most areas of 3D printing, cooling is ultimately about balance rather than maximum values. More fan speed is not automatically better. The best settings are simply the ones that allow the material to solidify fast enough to hold shape while remaining hot enough to bond strongly between layers.