Switching Materials: When and Why to Purge

3D Clean is designed for material changes. Leftover plastic from the last material is the most common cause of partial clogs and odd print defects.

High-temperature to low-temperature materials

This is the most important case. Between the hot melt zone and the cool heat break is a "gummy" zone. When you switch to a lower-temperature material, the old material in that zone never gets hot enough to flow out. It coats the inside of the hotend, the new material sticks to it, and flow is restricted. You may not notice until partway through a print.

Example: going from nylon to PLA. Even a thin coating of nylon inside the hotend can start the PLA sticking and cause partial clogs.

PLA to Pro PCTG (and other mismatched pairs)

PLA is much less viscous than PCTG. When you print PCTG after PLA in the same hotend, the leftover PLA forms a thin skin around the PCTG, like a sausage casing. PLA and PCTG don't bond to each other, so that skin ruins the PCTG's layer bonding. Purging with PCTG alone gets most of the PLA out, but never all of it. Run some 3D Clean between them.

On multi-nozzle printers, keep PLA and PCTG in separate nozzles. See Supports and PLA breakaway interfaces.

Sticky colors

Some colorants, especially certain dark reds and dark blues, linger in the hotend. You think it's clean, then hours into a white print a streak of the old color shows up. Purging with 3D Clean prevents this.

Filled and abrasive filaments

Wood-filled, glow-in-the-dark, and fiber-filled filaments leave particles behind. See Purging filled filaments.