The flow is the volume of filament that passes through the extruder based on the decided printing parameters to make a 3D model.
I usually set it from 90 to 125%, according to the structure I want to create.
For example, the same object that weighs 10 gr with a flow rate of 100% can change to 9 gr when the flow goes to 90%.
Now, let’s do some practice.
Import into Cura3D a generic file. I suggest a small cube. Set the parameters as follows:
It weighs 10 gr. Now, we keep the same parameter, but we change the Flow:
Setting the Flow to 90% makes the same object weight 90gr.
What does it change? It’s more fragile, but it has a better surface finish. The geometry doesn’t change that much, it’s pretty much the same as with a 100% flow rate.
Let’s see what happens when we increase the flow:
It’s the very same object as above, it only changes the flow rate.
Given the experience, I matured in this field, I can tell you each filament manufacturer has its own parameters. There are materials with Flow rate 95% and others, like flexible materials, with a 125% Flow rate.
In a nutshell: a low flow rate creates weaker objects, but with a high surface finish. A high Flow creates a stronger object, but with poor surface quality.