Foaming PLA (LW-PLA): set density with nozzle temperature, and what you give up
PLA that foams in the hotend: hotter means lighter, great for gliders and cosplay. Independent tests show less weight saved than claimed and strength falling faster.
- Foaming PLA carries a blowing agent triggered by nozzle temperature. An independent test saw foaming start near 215 °C and peak around 240–250 °C.
- Once it foams, cut the flow. Rough rule: flow ≈ 1 ÷ volume expansion. At 2.2× expansion, use about 45% flow.
- At 44% of normal PLA density, tensile strength drops to about a quarter and layer adhesion to about 13%. Use it for light parts that carry no real load.
- Retraction barely helps because the filament keeps foaming in the hotend. Use vase mode to cut stringing, and do not run a PTFE-lined hotend above 250 °C for long.
Foaming PLA (often sold as LW-PLA or lightweight PLA) contains a blowing agent that activates with heat in the hotend. The extruded line puffs up with tiny bubbles, the part gets much lighter, and you choose how light with the nozzle temperature. It is a natural fit for gliders, RC planes and cosplay. Independent testing, though, shows it saves less weight than advertised, and it loses strength faster than it loses weight.
Numbers here come from maker datasheets and an independent test on a bed-slinger with a 0.4 mm nozzle. Brands differ; treat the figures as a guide, not fixed values.
How the foam forms and why temperature controls it
The blowing agent releases gas once it gets hot enough, and more of it the hotter it gets, so the line swells more and density drops. One datasheet adds that the foaming ratio also depends on print speed and the size of the hotend’s melt zone: the longer the plastic stays hot, the more it foams.
| Source | Foaming starts | Maximum foaming / lowest density |
|---|---|---|
| Maker 1 | around 230 °C | up to 65% lighter, nearly 3× volume, 0.40–0.48 g/cm³ |
| Maker 2 | not stated | 220% volume, as low as 0.54 g/cm³ |
| Independent test (maker 1’s filament) | around 215 °C | around 240–250 °C, volume just over 2× |
Note that maker 2’s mechanical figures come from injection-moulded test bars, not foamed prints, so they cannot be compared directly with printed parts.
Independent test: how much lighter, how much weaker
The test printed three sets of samples on one printer from one spool: 205 °C (no foaming), 225 °C and 250 °C.
| Property | 205 °C, unfoamed | 225 °C (67% density) | 250 °C (44% density) |
|---|---|---|---|
| Horizontal tensile strength | 49 MPa | 24 MPa | 12 MPa |
| Layer adhesion | about 2/3 of horizontal strength | 13 MPa | 4.3 MPa |
| Hook load | 59 kg | 30 kg | 17 kg |
| Bending modulus (stiffness) | 3,200 MPa | 1,600 MPa | 900 MPa |
For impact, horizontal samples were tougher than regular PLA, close to a tough PLA. Upright samples absorbed about the same energy however much they foamed.
Weight drops to 44%, but tensile strength drops to about 24% and stiffness to about 28%. Half the weight does not mean the same strength per gram.
That is how porous foams behave: strength and stiffness fall faster than density (the Gibson-Ashby relationship used to describe foams). The tester’s conclusion was that the material suits light, non-critical parts.
Worked example: setting flow and predicting weight
Say a glider wing would weigh 100 g in regular, unfoamed PLA.
- Set the flow. If the line swells to 2.2× its volume while the slicer extrudes the normal amount, every line comes out fat. Cut the flow so the foamed line matches what the slicer planned: flow ≈ 1 ÷ 2.2 ≈ 0.45 (45%). That matches the datasheet example of a 45% first-layer extrusion rate at 270 °C.
- Predict the weight. At 44% of regular PLA density, the wing weighs about 100 × 0.44 = 44 g. The tester confirmed part weight scales with flow.
- Predict the strength. Tensile strength falls to about 12 ÷ 49 ≈ 25%, stiffness to 900 ÷ 3,200 ≈ 28%. The wing is more than half lighter but bends nearly four times as easily, so it needs a spar or internal structure.
The right flow has to be found on your own printer. The tester printed single-wall samples and measured wall thickness several times, the same as the flow step in tuning a new filament, and it changes again whenever temperature or speed changes.
Printer settings
From two makers’ datasheets:
| Setting | Recommended range |
|---|---|
| Nozzle | 190–270 °C (one maker) / 195–260 °C (the other) |
| Bed | 45–60 °C |
| Speed | 40–100 mm/s |
| Part fan | 100% |
Also worth knowing:
- First layer. One datasheet says to print the first layer at the same speed as the rest, with the same reduced extrusion rate, because a slower first layer stays hot longer and foams differently.
- Retraction barely works. The filament keeps foaming in the melt zone, so some stringing is normal. The tester raised retraction and the nozzle clogged above about 2.5 mm. The maker suggests vase-mode aircraft models, where the nozzle hardly ever travels across gaps.
- PTFE-lined hotends. Most should not run above 250 °C for long. For heavier foaming, use an all-metal hotend.
- Yellowing. Parts foamed hot can turn yellow; a lower temperature helps.
- Moisture. Store it like any PLA; see drying and storing filament.
Where it fits
- Glider and RC plane wings and fuselages. Lower wing loading means a lower stall speed. Load paths still need a spar or solid material.
- Cosplay helmets and armour. Big parts worn all day. The matte surface hides layer lines and takes paint easily.
- Ship models. One maker lists them among suitable uses.
Not a fit: motor mounts, brackets, load hooks, snap-fits, anything where stiffness matters.
Common mistakes
- Running hot without cutting flow. Fat lines, bulging surfaces, heavier parts than expected, wrong dimensions.
- Trusting the lightest number on the box. The independent test measured just over 2× expansion, not nearly 3×.
- Chasing stringing with ever-longer retraction. The strings stay; the nozzle clogs.
- Leaving the slow default first layer. It foams differently from the rest, sticks too hard or comes out the wrong size.
- Swapping it in for regular PLA on loaded parts. Half the weight, roughly a quarter of the strength.
Sources
FAQ
Can a PTFE-lined hotend print it?
Yes, at low to medium foaming temperatures. One maker's datasheet warns that most PTFE-lined hotends should not run above 250 °C for long; for more foaming, use an all-metal hotend.
Why did my part turn yellow?
Yellowing after high-temperature foaming is normal. A lower temperature reduces it, but the part foams less and weighs more.
Can I use it for load-bearing drone parts?
No. Strength and stiffness fall faster than weight. Use it for wing skins, fuselages or decorative shells, and keep motor mounts and other loaded parts in solid material.
Circuits and code were tested on sample boards. Boards differ in pin layout, so check your board's pinout before you power anything.