Every other material on this site has a density you look up. LW-PLA has one you choose. Its foaming agent expands when the plastic is hot enough, and how much it expands depends on the nozzle temperature and the flow rate you print at — so the same spool can produce a solid part or a part two-thirds air, and the number is a property of your profile rather than of the filament.
That single fact explains everything odd about this material, including why the slicer's weight estimate is wrong.
The range, and what it does to a kilogram
Stored density for LW-PLA runs from 0.4 to 1.24 g/cm³ — the spool sits at roughly PLA density and the printed part can be as light as the bottom figure.
Expressed as filament: a kilogram of 1.75 mm material at 1.24 g/cm³ contains 335.28 m of plastic. At 0.4 g/cm³ the same mass of printed material occupies the volume of 1039.38 m of solid filament — 704.1 m more, because a 210% density difference removes 67.742% of the volume from a given mass. That 1039.38 m is not filament anybody will ever wind onto a reel. It is the length of solid PLA the foamed material displaces, which is the honest way to describe what the weight saving buys, and entering 0.4 as the density in the length and weight converter reports the same thing for whatever mass you are printing.
Read practically: a part that weighs 90 g in solid PLA can weigh a third of that fully foamed. For a radio-control wing, a flying model, a prop or anything where mass is the design constraint, no other filament comes close.
Why the slicer lies to you about it
Slicers compute filament usage from a length of extruded material and a density you type in. With LW-PLA both halves of that are unstable.
The extruder pushes filament in at the flow rate you configured, and the material expands after it leaves the nozzle. So a profile that has not been corrected extrudes far too much plastic — the classic first LW-PLA print is a blobby, over-extruded mess. The standard fix is to drop the flow multiplier substantially, often to somewhere near a third, and the correct figure is specific to your temperature.
The stored weakness list names this directly: no slicer flow figure should be taken at face value. It also means the cost and weight estimates you get from a slicer are wrong until you have calibrated, which on a cost-conscious site is worth saying plainly.
The calibration you cannot skip
Printing LW-PLA well is a two-step process and the first step is not optional.
- Run a temperature tower, from around 200 °C to the top of the stored range at 260. Expansion increases with temperature, so each band of the tower is a different material.
- Pick the expansion you want — more foam is lighter and weaker, less foam is denser and stronger — and note the temperature.
- Calibrate flow at that temperature, by printing a single-wall test and measuring the wall thickness.
- Repeat when you change spools, because formulations differ between brands.
That is an afternoon before you print anything useful. Plain PLA needs none of it.
The four costs of printing air
Dimensional accuracy. The expansion ratio is calibrated per printer and per temperature, so the finished dimensions inherit whatever the temperature tower told you. Designing a press fit in a material whose size depends on a setting is not a fight worth having.
Surface finish. Foamed parts are matte and slightly rough, and the texture varies with the local expansion.
Strength. Tensile drops to 10–35 MPa against plain PLA's 45–65. The lighter you print it, the weaker it is — which is the entire trade and it is a fair one, since the part is being made lighter on purpose.
Price. $40–70 per kilogram against $15–28.
Drying. LW-PLA needs 45 °C for 4 to 6 hours, and the reason is unusual: moisture interferes with the foaming reaction itself, so a damp spool foams inconsistently. The result is a part with varying density, which for a wing is a balance problem rather than a cosmetic one.
Where plain PLA is the obvious answer
Everything that is not mass-constrained. If the part sits on a shelf, bolts to a wall, holds a tool or gets handled, its weight is irrelevant and plain PLA is cheaper, stronger, more accurate and needs no calibration.
Plain PLA is also the right choice for a first print of an LW-PLA design. Print it in the cheap material, confirm the geometry, and only then spend the expensive spool and the calibration time.
Where LW-PLA is the only sensible choice
- Fixed-wing model aircraft. The application it was created for, and vase-mode wing sections in LW-PLA are the reason it exists.
- Large props and costume pieces that have to be worn for hours.
- Anything flown, thrown or carried, where every gram is paid for repeatedly.
- Parts that need to float, which fully foamed PLA does easily.
Outside that list it is an expensive way to make a weaker part. Inside it, there is no substitute — and the honest way to decide is to ask whether anyone will ever notice the weight. If not, use plain PLA or a toughened blend and keep the afternoon.