Why does small PLA stick fine while large PLA parts lift at the corners?

A large part shrinks more in total, so the pull at each corner is bigger, and sharp corners are where that force concentrates. Add a brim, round or chamfer the base corners, keep the fan off for the first layers, and keep air-conditioning draughts off the printer.

Do I need glue stick for every material?

No. Prusa says PLA on a clean PEI sheet needs none. Glue stick is for PETG, ABS, ASA, nylon, PC and flexibles. For PETG on smooth PEI it works as a release layer, so the part does not bond so hard that it damages the sheet.

Raft or brim, which one?

A brim is a thin single-layer skirt attached to the base; it peels off easily, so try it first. A raft is a multi-layer slab under the whole part. Use it for tiny footprints or an uneven bed, at the cost of time, filament and a rougher underside.

Prints lifting off the bed: fixing adhesion and warping step by step

An hour into a print a corner has curled up off the bed, or the whole part is gone and the nozzle is dragging spaghetti around. That is warping and poor bed adhesion, the number-one problem when starting with FDM, and nearly every case is fixable without buying anything. This lesson goes through the fixes in order: free ones first.

The previous lesson, bed leveling and the first layer, covered nozzle height. Here we assume the first layer is squished correctly and the part still lets go.

Why plastic lifts

Plastic leaves the nozzle at 200–260 °C and shrinks as it cools to room temperature. Each new layer shrinks after the one beneath it, so it pulls the lower layer in toward the centre of the part. That force adds up layer after layer and concentrates at the base corners. When the first layer’s grip on the bed is weaker than the pull, the corner lifts.

That explanation gives you three groups of levers:

First-layer grip: how clean the bed is, how warm it is, how much area touches it (brim).
How much shrinkage: which material (ABS shrinks more than PLA) and how big the part is (a big part shrinks more in total).
How fast it cools: fan too strong, air-conditioning draughts, an open window, enclosure or not.

Warping is not just “the bed is bad”. It is a balance between the pull from shrinkage and the grip at the base. You can work on both sides.

Plastic shrinks as it cools; sharp corners get pulled up first

The fixes, free ones first

1. Clean the bed

The most common cause is fingerprints and grease. The Prusa Knowledge Base says to wipe with isopropyl alcohol (IPA) at 90% or higher. If IPA does not shift it (sugar, oil), wash the sheet with a few drops of dish soap in warm water and dry it completely. No wet wipes or tissues (fabric softener), and no bare fingers on the surface afterwards.

A smooth PEI sheet loses grip after a few hundred hours; an occasional acetone wipe restores it, on smooth sheets only. Textured and satin sheets must never see acetone.

2. Check nozzle height and first-layer speed

Round, unsquashed first-layer strands will not stick; see the previous lesson. But do not fix adhesion by lowering the nozzle further and further: Prusa warns that too low damages the sheet and voids the warranty.

A slow first layer helps. Prusa suggests about 75% speed for the first three layers; check a fast profile has not pushed “First layer speed” up.

3. Bed temperature by material

The ranges below come from Prusa’s and Polymaker’s material guides. Start inside them, then check the datasheet of the filament you actually use.

Material	Bed	Nozzle	Enclosure	Glue stick
PLA	50–60 °C	185–235 °C	No	Not needed on a clean bed
PETG	70–90 °C	230–250 °C	No	As a release layer on smooth PEI
ABS	80–110 °C	about 255 °C	Recommended	Yes
ASA	100–110 °C	about 260 °C	Recommended	Yes
Nylon (PA)	70–100 °C	per datasheet	Recommended on open printers	Yes
PC	90–120 °C	per datasheet	Required	Yes

If a new filament sticks poorly, Prusa suggests raising the bed 5–10 °C at a time, but not endlessly: an overheated bed softens the lower layers so they bulge outward (elephant foot), and PLA much above 65 °C starts to distort.

A note on PETG: it bonds to smooth PEI too well, and peeling the part can tear the coating off the sheet. Prusa recommends a textured or satin sheet, or a thin film of glue stick on the smooth sheet as a release layer.

4. Fan and draughts

The part-cooling fan makes upper layers shrink faster, which is why profiles keep it off for the first layers; Polymaker suggests no cooling for the first 0.5–0.7 mm. For ABS/ASA keep the fan very low or off except on small features.

Air from an air conditioner, a room fan or an open window cools one side of the part faster than the other. Prusa names draughts as a direct cause of warping. Move the printer out of the airflow before thinking about an enclosure.

Skirt, brim, raft: which one when

All three live on the “Skirt and brim” page in PrusaSlicer; OrcaSlicer and Bambu Studio have the same options under similar names.

Option	What it is	Use when	Downside
Skirt	Loops around the part, not touching it	Every print: primes the nozzle and lets you check the first layer before the real part	Does not add grip
Draft shield	A skirt as tall as the part, a wall against draughts	ABS/ASA/PC on a printer without an enclosure	Time and filament
Brim	A thin single-layer flange spreading out from the base	Tall parts with small bases, sharp corners, many small parts	Must be peeled; leaves a mark on the bottom edge
Raft	A multi-layer slab under the whole part	Tiny footprints, an uneven bed, high-shrink materials	Slow, wasteful, rougher underside

Prusa recommends a brim at least 3 mm wide, and to try a brim before reaching for glue or adhesion sprays. If it is hard to peel, set “Brim separation gap” to about 0.1 mm so there is a hairline gap between brim and part.

OrcaSlicer also offers Mouse ears: small discs only at sharp corners instead of a brim all the way round, and an Auto brim that sizes the width from the geometry (capped at 18 mm). Without either, Prusa suggests the manual version: add a small cylinder a few layers tall at the problem corner in the model and cut it off after printing.

Worked example: a 120 mm ABS box with lifting corners

A common real case: an ABS box, 120 × 80 mm footprint, straight walls, square corners, printed on an open printer with the bed at 100 °C. Forty layers in, all four corners have lifted about 2 mm.

In order:

Enclosure. An open printer and ABS this size is hard from the start. Prusa says plainly that large ABS parts need warm surrounding air. With no enclosure yet, enable Draft shield and turn the part fan off for the whole job.
Bed. Raise it to 105–110 °C (Prusa runs 105/110 for ASA and says bigger parts want more).
Base. A thin film of PVA glue stick on the PEI sheet, then a brim of 8–10 mm, or mouse ears at the four corners.
Design. If you can edit the model, replace the square base corners with a 3–5 mm radius or a 45° chamfer. Rounded corners spread the pull instead of concentrating it at one point.
Speed. Slow down. Each layer gets more time to bond to the one below and shrinks more gradually.

The first four usually suffice. If not, print a 60 × 60 × 5 mm test slab to find a combination that holds before spending a whole box of filament.

Safety

A bed at 100–110 °C is hot enough to blister. Do not peel parts bare-handed while the bed is hot; let it cool first. Many parts release on their own as the bed cools.
ABS/ASA give off fumes you should not breathe. Ventilate the room, but without blowing air at the printer (Prusa stresses this). An enclosure vented outside answers both.
A hot enclosure over long prints can distort the printer’s own plastic parts, such as fan ducts.
Acetone is flammable; keep it away from the hot bed.

Common mistakes

Lowering the nozzle again and again instead of cleaning the bed. You get a splayed first layer and a scratched sheet; the real problem was grease.
Using wet wipes or 70% IPA. They carry oils and additives and leave a film instead of removing one.
A thick layer of glue over the whole sheet. Thick glue is a slippery layer. A thin, spread film is enough, and an ordinary PVA stick will do; no hot glue, no super glue.
Fan at 100% from layer one with PETG/ABS. The lower layers cool too fast and start pulling on the base immediately.
The air conditioner pointed at the printer. Same printer, same settings, new room, parts let go: the draught.

The next lesson, overhangs and bridging, is where that same fan does the opposite job: cooling plastic that hangs in the air before it sags.

Sources

Circuits and code were tested on sample boards. Boards differ in pin layout, so check your board's pinout before you power anything.