There is no specification called PLA+. No standards body defines it, no test has to be passed to print it on a label, and two spools carrying the same name from different brands can contain different additive packages doing different things. That is the first thing to know, because it explains why forum arguments about PLA+ never resolve: the participants are not describing the same material.
What is usually in the box is base polylactic acid plus an impact modifier — a small fraction of a rubbery polymer dispersed through the matrix, exactly the trick ABS uses, at a much lower loading. Some brands add a nucleating agent to speed crystallisation, some add flow aids to make the material run smoother at speed, and some add a bit of everything.
The property that genuinely improves
Toughness, in the specific sense of energy absorbed before fracture. Drop a plain PLA bracket on a hard floor and it can shatter along a layer line; the same part in a good PLA+ tends to survive, or to crack rather than explode. Elongation before break rises. Screw bosses tolerate being over-tightened. Thin snap features flex a little instead of snapping off on first use.
That is a real and useful improvement, and for functional parts it is worth paying for.
The property that does not improve, whatever the name suggests
Heat resistance. PLA+ softens between 52 and 62 °C, which is the same territory as plain PLA and for the same reason: the base polymer's glass transition has not moved. An impact modifier at a few percent loading does not change where a chain starts sliding past its neighbours. A PLA+ part on a car dashboard sags on the same afternoon a PLA one does.
Tensile strength usually does not improve either, and often goes slightly the other way — the stored range for PLA+ tops out at 60 MPa against plain PLA's 65. Adding a soft phase to a stiff matrix trades peak strength for toughness. That is the deal, and it is a sensible deal, but "stronger" is the wrong word for it and the wrong word is what sells the spool.
If a brand claims a higher heat resistance, ask for the data sheet and check which test it used. Heat deflection at a low load flatters every material, and the number quoted is often not the one that governs a part sitting in a warm car.
What the added viscosity does to your profile
The recommended window — 205 to 230 °C at the nozzle, 50 to 65 °C on the bed, no enclosure — sits a few degrees above plain PLA's, and the offset is not arbitrary. The impact modifier raises melt viscosity, so pushing the same volume through the same nozzle needs a little more heat, and without it the extruder starts skipping on fine features.
Two consequences follow from the same viscosity change:
- It strings more. Retraction settings carried over from plain PLA usually need a small increase in distance, and a slower travel speed helps more than people expect.
- Fine detail comes out softer. Sharp text and small raised features round off slightly. For a display model, plain PLA is still the better print.
First-layer behaviour is the one place PLA+ is easier: it tolerates a slightly wrong Z offset better than plain PLA, because the tougher melt smears rather than tearing.
What the premium actually costs
Hold everything constant except the spool price. A 150 g part, 6 hours, a machine drawing 100 W, machine wear at $0.30 an hour, a 5% failure rate and 0.6 kWh of electricity at the US average — that fixes $1.80 of machine time and $0.11 of power whichever spool is loaded. At $20 a kilogram the plastic is $3.00 and the job is $5.16; at $26 a kilogram it is $3.90 and the job is $6.11.
Ninety-five cents. That is the entire argument, and on a functional bracket it is obviously worth it — the toughening costs less than a fifth of the print. Across a batch of fifty display models it is close to fifty dollars spent on a property nobody will ever load. Run your own prices through the print cost calculator; only the filament term moves, which is exactly why the comparison is easy to make.
What PLA+ is genuinely bad at
- Anything warm. Cars, windowsills, enclosures, near a heated bed, next to a power supply.
- Sunlight. The base polymer still degrades under ultraviolet, goes chalky and then brittle. The modifier does nothing about it.
- Fine detail and crisp text, for the viscosity reason above.
- Being a substitute for a real engineering material. If a part needs both toughness and heat, the answer is a copolyester or a styrenic, not a tougher PLA.
- Being compared honestly between brands. With no standard behind the name, the only reliable test is printing the same part in two spools and breaking both.
Where it is the right call
Printed tools, jigs handled daily, brackets that get knocked, enclosures for hobby electronics, RC parts that land badly, toys for children who throw them, and anything that will be assembled with self-tapping screws. Anywhere the failure you actually fear is a sudden brittle crack rather than a slow sag, PLA+ is the sensible default and the price difference is noise.
For the case where you want to know exactly which properties diverge from plain PLA and which are marketing, the side-by-side comparison works through it property by property.