Full brims can improve first-layer adhesion, but they also create unnecessary post-processing when only one or two areas of a 3D printed part are actually trying to lift. Lily pads, sometimes called mouse ears, apply additional adhesion exactly where the geometry and polymer behavior require it.
You finish a print, pull it from the build plate, and the part looks excellent. Then you notice the bottom perimeter.
A full brim has left a rough edge around every surface that touched it. Now the flush cutters, deburring tools, and sandpaper come out.
For a PLA prototype, that cleanup might take a minute. For production parts or high-temperature engineering polymers, the labor adds up quickly. The bigger problem is that much of the brim may never have been necessary.
In many warping problems, the entire perimeter is not trying to separate from the build plate. One sharp corner, thin section, or thermally stressed region is generating the problem.
That changes the adhesion strategy.
Why Do 3D Printed Parts Warp at the Corners?
Warping is fundamentally a dimensional stability problem. Extruded polymer is deposited at elevated temperature and contracts as it cools. If that contraction is constrained by the build plate, previously deposited material, or surrounding geometry, residual stress develops in the part.
Corners are particularly vulnerable because geometry concentrates the effect of shrinkage from multiple directions. Sharp transitions, thin sections, and long straight toolpaths can further increase local stress.
If the upward force generated by the contracting part exceeds the effective adhesion between the first layer and build surface, the corner lifts.
Semi-crystalline polymers add another variable. Materials such as PEEK undergo crystallization as they cool. Crystallization is associated with additional volumetric change and can increase dimensional control challenges when thermal conditions are not sufficiently managed.
The exact shrinkage and crystallization behavior depends on polymer grade, reinforcement, cooling history, chamber temperature, and processing conditions. It is therefore more accurate to treat PEEK warping as a thermal-process problem rather than assigning a single universal shrinkage value to the material.
What Is the Difference Between a Skirt and a Brim in 3D Printing?
Skirts and brims are often grouped together in slicer settings, but they solve different problems.
A skirt is printed around the part without touching it. Its primary value is process verification. You can observe extrusion consistency, nozzle flow, first-layer positioning, and obvious build plate alignment problems before the printer commits to the actual component.
This is especially valuable when printing expensive engineering polymers. Discovering a first-layer problem during a few skirt loops is significantly cheaper than discovering it several hours into a PEEK or PEI print.
A brim physically connects to the first-layer perimeter of the part. By increasing the effective bonded area around the component, it provides additional resistance against lifting.
Brims work. The tradeoff is that every millimeter of attached brim becomes a potential post-processing operation.
Why Do Full Brims Create Unnecessary Post-Processing?
Consider a wide component with a large first-layer perimeter. If only one corner is experiencing enough residual stress to lift, a full brim still attaches to the entire perimeter.
You have increased adhesion in dozens of locations that did not require additional holding force.
Once the print is complete, that excess material must be removed. Depending on the polymer and first-layer tuning, brim removal can leave a rough edge that requires cutting, scraping, deburring, or sanding.
Parts with multiple feet, pads, or disconnected first-layer regions make the problem worse. Instead of removing one continuous brim, you may be cleaning multiple small attached features.
The engineering question is not simply, “How do I increase bed adhesion?”
A better question is, “Where does this part actually need additional resistance to lifting?”
What Is a Lily Pad or Mouse Ear in 3D Printing?
A lily pad is a small, flat sacrificial disc placed at a specific region of a part that is susceptible to lifting. The same general technique is often called a mouse ear.
Mechanically, a lily pad is a localized brim.
Instead of increasing adhesion around the complete perimeter, the disc increases first-layer surface area at a selected corner or feature. Part of the disc overlaps the model while the remaining area extends onto the build plate.
The overlap connects the lily pad to the printed component. The exposed portion creates additional bonded area with the build surface.
After printing, you remove one small sacrificial feature instead of cleaning the complete bottom perimeter.
This is targeted adhesion rather than perimeter-wide adhesion.
When Should You Use Lily Pads Instead of a 3D Printing Brim?
Lily pads make the most sense when warping is localized and repeatable.
If previous prints consistently lift at the same corner, that location is an obvious candidate. Sharp corners, narrow extensions, thin sections, and regions influenced by long directional toolpaths may also justify targeted adhesion.
Lily pads are particularly useful with high-performance thermoplastics where thermal contraction and, for semi-crystalline polymers, crystallization behavior can generate significant residual stress.
PEEK is an important example because it is a semi-crystalline thermoplastic. PEI materials commonly sold under the ULTEM™ trade name are amorphous rather than semi-crystalline, so their warping mechanism should not be described as crystallization. They can still develop substantial thermal stress and dimensional distortion during cooling.
PSU and PPSU are also amorphous polymers, while nylon behavior varies significantly by chemistry, reinforcement, moisture condition, and processing history.
The practical result is similar: if a specific region repeatedly lifts, localized first-layer reinforcement can improve print stability without creating a full perimeter cleanup operation.
How Do You Create a Lily Pad in PrusaSlicer?
The technique can be created directly in PrusaSlicer using a basic geometric primitive. Similar workflows are available in OrcaSlicer and Bambu Studio, although menu names and object operations may differ between software versions.
- Disable the full brim. Open the skirt and brim settings and set the brim type to no brim.
- Keep the skirt enabled. Two or three loops are a practical starting point for observing extrusion and first-layer behavior. Additional loops may be useful when more process observation or nozzle purging is required.
- Add a cylinder primitive. Right-click on the build plate, select the option to add a shape, and insert a cylinder.
- Unlock independent scaling. The X, Y, and Z dimensions need to be adjusted independently.
- Set the Z dimension to the intended lily pad thickness. For a single-layer lily pad, match the Z height to the first-layer height. For example, a 0.24 mm first layer would use a 0.24 mm thick disc.
- Set the disc diameter. Approximately 20 mm is a reasonable starting point, not a universal specification. Larger discs provide more build plate contact area but also create a larger sacrificial feature.
- Position the disc over the problem area. Move the lily pad so that it overlaps the corner while still extending onto the build plate.
- Merge or group the objects as required by the slicer. Verify in the sliced preview that the lily pad and component form the intended connected first-layer geometry.
The sliced toolpath preview is the final authority. Do not assume that two objects are connected simply because they visually overlap in the 3D editor.
How Much Should a Lily Pad Overlap a 3D Printed Part?
A useful starting point is to position the disc so that a substantial portion overlaps the corner while the remaining area contacts the build plate.
Roughly half-overlapping the corner is a practical rule of thumb, but it should not be treated as a fixed engineering specification.
Too little overlap can create a weak connection between the lily pad and the component. Too much overlap reduces the additional build plate area and may make removal more difficult.
The optimum geometry depends on the polymer, first-layer height, extrusion width, adhesive system, build surface, and magnitude of the lifting force.
For a production process, document the successful lily pad diameter, thickness, and placement as part of the qualified slicer configuration rather than recreating the geometry by eye for every build.
Can Bed Adhesive Eliminate the Need for Brims?
A properly selected build surface and adhesive system can eliminate the need for additional adhesion features on many geometries. Claims that a specific percentage of parts will print without a brim, however, should be treated as application-specific rather than universal.
Adhesion performance depends on the polymer, surface preparation, build plate material, bed temperature, first-layer process parameters, component geometry, and thermal environment.
Nano Polymer Adhesive was originally developed for difficult engineering polymers including PEEK, PEI, and PPSU. With an appropriate heated build surface, it can provide the primary adhesion mechanism while lily pads are reserved for geometries that still exhibit localized lifting.
The adhesive is commonly used on heated beds, but references to an exact “activation temperature” should be understood as product-specific process guidance rather than an industry-standard polymer threshold. Follow the current adhesive manufacturer’s processing instructions for the selected material and build surface.
This leads to a useful process hierarchy:
- Establish a stable first layer and controlled build surface.
- Use an appropriate bed adhesive when required.
- Print without a brim when the geometry remains stable.
- Add lily pads only at repeatable lifting locations.
- Use a full brim when the lifting behavior is distributed around a larger portion of the perimeter.
Why Does PEEK 3D Printing Require More Thermal Control?
PEEK is governed by more than nozzle temperature and bed adhesion. Its semi-crystalline structure means cooling history affects crystallization, morphology, shrinkage, and final part properties.
ISO 11357 provides differential scanning calorimetry methods used to characterize thermal transitions and crystallization behavior in plastics. ASTM D3418 is also commonly used for DSC measurement of transition temperatures and enthalpies of fusion and crystallization.
These standards do not provide a universal “correct” PEEK printing temperature. They provide methods for measuring thermal behavior. Actual additive manufacturing process parameters remain dependent on the polymer grade, machine architecture, component geometry, and required final properties.
This is why a lily pad should be viewed as a localized mechanical countermeasure, not a substitute for thermal process control.
If a PEEK component is warping across multiple regions, repeatedly delaminating, or showing severe dimensional distortion, adding larger and larger lily pads is unlikely to address the root cause. Chamber temperature, bed temperature, thermal gradients, material condition, toolpath strategy, and cooling history should be evaluated.
How Do You Reduce Post-Processing on Engineering Polymer 3D Prints?
The fastest post-processing operation is the one you eliminate before printing.
A full brim is a broad solution. Lily pads convert that broad solution into a localized process control.
For one-off prototypes, the difference may only be a few minutes with flush cutters and a deburring tool. Across repeated production builds, those minutes become labor hours. Additional hand finishing also introduces another opportunity for inconsistent edge quality or accidental part damage.
The goal is not to eliminate brims from every print. Some geometries genuinely benefit from continuous perimeter reinforcement.
The goal is to stop applying a full brim automatically.
Start with a controlled build surface and appropriate adhesion system. Observe where the component actually lifts. Add adhesion area at those locations. Then verify the result in the slicer preview and document the successful configuration.
When only one corner is causing the problem, you should not automatically commit yourself to cleaning the entire perimeter.