What’s the problem with PLA again?

Polylactic Acid (PLA) is one of the most popular and widely used filaments in FDM printing, but it’s just one of the many thermoplastics available. When I was starting out over a decade ago, PLA and ABS were the only options available for consumer FDM printing.

PLA was easier to print without issues, while ABS was the more engineering-grade material, with better environmental, impact, and thermal characteristics. A pro/con list from back then would probably have looked something like this:

Pros of Using PLA Filament

1. Easy to Print With
   It doesn't require a heated bed, and it prints well at low extruder temperatures (210°C). PLA is also less prone to warping or curling compared to other materials.

2. Low Odor and Fumes
   During the printing process, PLA emits very minimal odor, unlike ABS, which can release strong, unpleasant fumes.

3. Available in a Wide Range of Colors and Blends
   PLA comes in a vast array of colors, finishes, and specialty blends. From matte and glossy to glitter and glow-in-the-dark, you can find PLA filaments that suit almost any design aesthetic. Some manufacturers even offer PLA mixed with materials like wood or metal for unique textures and finishes.

4. Good Surface Finish and Detail

Cons of Using PLA Filament

1. Lower Heat Resistance
   PLA has a relatively low glass transition temperature (around 60°C), meaning it can start to soften or deform under heat. This makes it unsuitable for objects exposed to higher temperatures.

2. Brittleness
   While PLA is strong and rigid, it tends to be more brittle than other filaments like ABS or PETG. This can result in cracking or breaking under stress, especially if used for functional parts that require flexibility or impact resistance.

3. Limited Durability
   PLA’s biodegradable nature, while environmentally friendly, also means it’s not as durable as other plastics over long periods, especially in outdoor or humid environments. Prolonged exposure to moisture and UV rays can cause the material to degrade or lose strength.

4. Not Suitable for Mechanical Parts
   PLA’s lack of flexibility and heat resistance makes it a poor choice for mechanical parts or moving components. If your project requires parts that need to withstand friction, force, or heat, a more durable filament like PETG or Nylon might be a better option.

5. Difficult to Post-Process
   While PLA produces a smooth surface finish, it can be harder to post-process compared to other materials. It doesn't sand or polish as easily as ABS, and its low melting point makes it more difficult to use with acetone smoothing or other chemical treatments.

One thing that jumps out at me, is that this list looks reasonable, but it’s definitely outdated. Both printer and material technology advancements have affected both the relative pros and cons of PLA.

Whereas PLA used to be very easy to print, relative to other filament types, printer and slicer advancements have made ALMOST ALL filaments easy to print. Assuming your material settings are good, your filament is properly prepared, and you have a printer that’s appropriate for the bed/extruder/chamber temperatures you need, printing is largely a click-and-go experience now. So, PLA is not any more difficult to use now, but everything else (except some of the more exotic engineering materials) is much easier to use than it was before.

PLA is available in all of the colors of the rainbow. Silk, matte, translucent, metallic, and virtually anything else you can imagine. That said, the filament industry has created similar (though still smaller) product landscapes for ABS and PETG, too.

Many of the cons of PLA have been addressed, at least in part, with formulations like PLA+ and Tough PLA. Post-processing remains an issue, but it somewhat minimized with better releasing supports (slicer advancements), better bridging performance (printing improvement), and multiple filament support through AMS-like systems or multiple toolheads (being able to use separate breakaway support filament).

I feel like it is safe to say that prints exposed to heat or the outdoors are still poor candidates for PLA.

Specialty colors and finishes are still probably squarely the domain of PLA. Its hard to imagine getting my oddball gradient/2 color/3 color filaments in anything but PLA.

For everything else, though, I think it’s probably worth considering a closed volume printer, and using PETG or ABS. Filament variety is pretty good for either, and the prices are comparable.