How do I heat treat?

Heat treating must be done after printing because the crystalline structure is reset to amorphous when melted. Here's what you'll need to get started heat treating:

• An oven - ideally large and with good temperature control/stability
• Aluminum foil - in case you have a small oven or one with glowing coils
• A flat wood block or cutting board OR silicone surface on flat baking sheet
• HTPLA filament and/or parts with supports if required

Preheat your oven to 95-120 C (200-250 F). Protopasta recommends a convection oven set at 225 F. If using an electric oven, judge when the coils are no longer glowing. If glowing coils can't be avoided, block them with a foil sheet. Insert a flat and rigid wood or silicone surface in the oven. Once preheated, place your part on the wood or silicone surface and bake until the material is has changed (usually about 10 minutes).

While fiber reinforced materials can give the best result when heat treating, translucent materials are best for observing the change. You'll see the translucent materials turn opaque when heat treated.

What temperature should I print it at??

That depends greatly on your hardware and other settings. It's sometimes reported that a wide range of temperatures do not work, but with proper hardware, setup, and settings, a wide range of temperatures (205-235 C for example) can create comparable results using HTPLA. Layer thickness, extrusion width, speed, and flow settings can all have a very strong influence on results. Not to mention first layer adjustment, overlap settings, and hardware choice/modifications.

For machines with all metal hotends, you need to keep the print rate up for a good experience. That means printing with thicker layer and/or larger nozzles to avoid jamming and/or unnecessarily high temperatures. With a teflon-lined hotends, you can print a lower rates and at lower temperatures without the same risk of jamming. Bowden tubes machines can lack enough push for high print rates, but also don't provide enough force for a bad jam. Direct drive can push high flow rates or hard to remove jams.

It's all these hardware variations that make it difficult to choose a single, ideal set of parameters. General parameters- based on a standard 0.4 mm nozzle spanning Prusa MK3 and Creality Ender 3, all-metal and teflon-lined, bowden and direct drives, recommended to aim for about 3 +/- 1 cu mm/s volume rate for printing. With a 0.44 mm extrusion width and 0.22 mm layer thickness, that's about 20-40 mm/s speed. 20 mm/s should give a good surface finish but risk being on the slow side for all metal hotends while 40 mm/s infill can approach the maximum rate for Creality's bowden with 0.4 mm nozzle.