Perhaps the most common question we get from new 3D printer owners is, “How do I get rid of oozing and stringing on my prints?”

Extruding thermoplastic is a complicated process with dozens of variables in play. However, understanding what causes oozing/stringing on your prints doesn’t have to be that complicated.

What is Retraction?

First, let’s start with the most common misconception about what retraction does and how it works.

Myth - Retraction “sucks” filament back up through the hot end. So, the more retraction you use, the less oozing you’ll get.

Fact – Once filament has melted in the “melt zone” of your hot end, it cannot be retracted. Retraction does not create negative pressure. Hot ends are not sealed/airtight. If they were, then the negative pressure would “suck” molten filament back up through the hot end. This would likely lead to lots of jams and other extrusion issues, but this is not the case.

Think about candle wax. If you were to put a small cylinder of wax into a pool of melted candle wax and then pull it out, would the melted wax come with it? Of course not. While a small amount of wax will stick to the cylinder when you remove it, it does not pull the pool of molten wax up with it.

In the same way, the solid filament above the melt zone does not retract the molten filament with it.

Ok, so if retraction doesn’t pull filament back up through the nozzle, what does it do?

The purpose of retraction is simply to relieve pressure from the melt zone so that filament isn’t being forced through the nozzle during non-print moves.

What are the Best Retraction Settings?

There is a lot of misinformation out there about how much retraction you should have. I’ve seen recommendations from .1mm all the way up to 20mm. So what is the correct amount?

The correct amount is the minimum amount required to reduce the most stringing on your part. Some machines and hot ends require more retraction than others, and each material has different requirements. In general, though, it’s unlikely you should need more than 5mm or less than 1mm.

Settings to Tune

There are a few other important settings that affect oozing/stringing on parts. We’ll go through the process of adjusting your machine to get the least amount of oozing possible, but it’s critically important that you start out with a properly calibrated extruder. If you haven’t calibrated your extruder before, read this before you start adjusting retraction settings.

There are only 2 settings we’ll be adjusting for retraction in this article: