A printed TPU gasket is a flat or ring-shaped seal made from flexible polyurethane filament that is squeezed between two parts so it fills the small gaps between them. It seals by being compressed, not by being stretched: design it so a groove holds it and it is squeezed by roughly 10–20% of its thickness (our starting point, see the design section), choose a 95A grade for your first attempt or 85A when the clamping force is low, and print it slowly with walls rather than infill.
A printed gasket is a practical fix for dust, splashes and rattle on a hobby enclosure, not a certified seal. FDM layers can leave leak paths, TPU takes a permanent set when it is warm, and Bambu Lab states that its TPU is not food-contact grade. The numbers below come from Parker’s O-ring handbook (written for rubber seals) and from the Stratasys, Polymaker, NinjaTek, Recreus, Prusa and Bambu Lab documents linked at the end; where a value is our starting point we say so.
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TPU gasket in six steps
- Pick the hardness: 95A is the easiest to print; 85A or softer seals with less clamping force but is harder to feed.
- Model a groove in one of the parts so the gasket cannot slide, with a depth that gives about 10–20% squeeze (starting point) and a width that leaves free space beside the gasket.
- Make the gasket’s width a multiple of your line width so the slicer fills it with perimeters only, with no infill gap inside.
- Dry the spool, then print the gasket flat and slowly, with the fan setting from your filament’s data sheet.
- Fit it, tighten the screws evenly against a hard stop, and test with water or the real working condition.
- If it leaks, change the squeeze or the walls first; temperature changes come last.
What a printed TPU gasket can and cannot do
Makers of flexible filament do list seals as a use: Stratasys names seals, protective covers and vibration dampeners as typical applications for its FDM TPU 92A, and Recreus lists buffers and gaskets for Filaflex. That fits low-pressure jobs such as a lid on an electronics box, a dust seal around a connector or a vibration pad. The same documents also show the limits:
| Limit | What the documents say | What it means for a gasket |
|---|---|---|
| Compression set | Stratasys FDM TPU 92A: 21% after 22 h at 23 °C and 44% after 22 h at 70 °C (ASTM D395). Polymaker’s PolyFlex TPU95 data sheet does not report it. | Compression set is the share of the squeeze that the material does not spring back from. It grows with temperature, so a gasket in a warm enclosure loses squeeze faster. This is industrial printer data, not a guarantee for hobby filament. |
| Heat | NinjaFlex data sheet: heat deflection temperature 44 °C at 0.45 MPa and 60 °C at 0.07 MPa. | Keep printed TPU gaskets away from hot parts and from sealed bodies that sit in the sun. |
| Chemicals | Polymaker rates TPU95 as good against oils and grease, fair against weak acids and alkalis, and poor against strong acids and alkalis. | Check your filament’s own chemical data before using a gasket with fuel, solvents or cleaners. |
| Water and air | Prusa’s watertight-prints guide needs extra perimeters, a hotter nozzle and more flow even for rigid filaments, and states that watertight does not mean food safe. | Treat a printed gasket as water-resistant until you have tested it. Do not use it on pressurised or food-contact parts. |
Shore hardness for a gasket
Shore A hardness is the number on the spool: higher is firmer. Parker’s handbook says a Shore A hardness of 70 to 80 is the most suitable compromise for most rubber seals. Printable TPU starts higher, because Bambu Lab only supports 85A and harder on its printers and Prusa notes that the softer the filament, the harder it is to print. The practical choice is therefore between roughly 85A and 95A, and it is mainly a trade between sealing force and printability.
| Hardness | Examples from maker data | Gasket behaviour | Printing |
|---|---|---|---|
| 82–85A | Recreus Filaflex 82A; NinjaTek NinjaFlex 85A | Conforms to rough faces with little clamping force | Direct drive recommended by both makers; Bambu Lab needs a 0.6 or 0.8 mm nozzle for 85A on its printers |
| 90A | Bambu Lab TPU 90A | Middle ground | Compatible with 0.4, 0.6 and 0.8 mm nozzles on Bambu Lab printers |
| 95A | Polymaker PolyFlex TPU95; eSUN eTPU-95A; Bambu Lab TPU 95A HF; NinjaTek Cheetah | Firmer, needs more clamping force for the same squeeze, holds its shape in thin lips | Easiest to feed; the best place to start |
| Below 85A | NinjaTek Chinchilla 75A | Very soft: seals well but deforms and tears easily | Not supported by Bambu Lab printers; see TPU vs TPE |
Designing the compression and the groove
Squeeze is the share of the gasket’s free thickness that is taken up when the parts are bolted together: squeeze % = (free thickness − compressed thickness) ÷ free thickness × 100. A 2.0 mm gasket pressed to 1.7 mm is squeezed by 15%. The compressed thickness should be set by a hard stop, such as the two parts touching around the groove, so the seal does not depend on how hard each screw is tightened.
- Squeeze. Parker’s handbook gives about 30% as the maximum static squeeze for most elastomers and about 16% for moving seals, and says squeeze should never fall below about 0.2 mm, because a very light squeeze quickly takes a full compression set. Those figures are for moulded rubber O-rings. For printed TPU we suggest starting around 10–20%, with at least 0.2 mm in absolute terms, and adjusting after a leak test. This is a starting point, not a published TPU value.
- Free space. Rubber is pushed sideways when compressed and needs somewhere to go. Parker recommends filling 60–85% of a gland (75% optimum) and leaving at least 10% void. The same logic applies to a rectangular printed gasket.
- Worked example (illustrative, not tested). A gasket 2.0 mm thick and 3.0 mm wide has a cross-section of 6.0 mm². Pressed into a 1.7 mm deep groove (15% squeeze), a 75% fill needs a groove 6.0 ÷ 0.75 ÷ 1.7 ≈ 4.7 mm wide. Parker’s guideline is for rubber O-rings, so treat the result as a first prototype.
- Stretch. Parker keeps the installed stretch of a ring to 5% or less, and notes that stretching also thins the cross-section. Make a ring gasket the size of the groove path instead of relying on TPU to stretch over it.
- Cross-section. A round section needs support or an overhang on a flat-printed ring, so a rectangular or slightly chamfered section is easier. Round every inside corner of a rectangular gasket with a fillet so the corner does not tear.
- Clamping force. A 95A gasket needs more force for the same squeeze than an 85A one. Use enough screws, close enough together, that the lid does not bow between them.
Print settings for a TPU gasket
Use the data sheet of your own filament first. Published settings differ, as the table shows, and the fan advice even contradicts itself: Prusa and Recreus switch the fan off, while Polymaker, NinjaTek (from layer 2), eSUN and Bambu Lab run it. Treat any value below as a starting point and dial it in with a temperature tower.
| Source | Nozzle | Bed | Speed | Fan |
|---|---|---|---|---|
| Polymaker PolyFlex TPU95 (TDS, 0.4 mm nozzle) | 210–230 °C | 25–60 °C | 30–50 mm/s | On |
| Prusa, flexible filaments in general | 230–245 °C | 60–75 °C | Typically 20 mm/s, 30–40 mm/s at most | Off |
| NinjaTek NinjaFlex 85A | 225–250 °C | Room temperature to 50 °C | Top/bottom 10–20 mm/s; infill and shells 15–35 mm/s | On from layer 2 |
| Recreus Filaflex 82A (0.4 mm nozzle) | 240 °C | Room temperature for small parts, 45–50 °C for large | Volumetric limit 3.2 mm³/s; first layer 30% of infill speed | Off |
| eSUN eTPU-95A (TDS) | 220–250 °C | 45–60 °C | 20–50 mm/s | 100% |
| Bambu Lab TPU 95A HF (TDS, high-speed grade) | 220–240 °C | 30–35 °C | Under 200 mm/s on Bambu Lab printers | On |
- Walls, not infill. Prusa’s watertight guide asks for at least 3–4 perimeters for a single wall, notes that very thick walls that need infill can leak into the gap between walls, and says a 0.2 mm layer height is fine as long as it stays at or below 60–65% of the nozzle width. Choose a gasket width that is a whole number of line widths and wall thickness settings that produce solid perimeters.
- Flow and temperature. The same guide raises the nozzle temperature by 5–10 °C and the flow by 5–10% for general filaments. With TPU, change one value at a time: Bambu Lab’s advice for oozing goes the opposite way, about 5 °C cooler.
- Orientation. Print a flat gasket flat. Its layer lines then run around the ring, parallel to the sealing faces, so compression closes the layers instead of pulling them apart. This is our reasoning rather than a measured result.
- Feeding. TPU is soft, so slow, direct-drive printing matters more than any gasket setting. The TPU jam guide covers tension, retraction, drying and why Bowden machines struggle.
- Drying. Maker values differ: 70 °C for 8 hours for Polymaker and Bambu Lab, 55 °C for more than 4 hours for eSUN, 55 °C for at least an hour for Recreus. Wet TPU strings and bubbles, which makes a leaky gasket.
Test it and fix leaks
Test the gasket in the orientation and under the conditions it will see: fill the box with water and leave it on paper towel, or press air in with a hand pump and brush on soapy water. A quick look is not a test. Then match the failure to a cause:
| Symptom | Likely cause | Fix |
|---|---|---|
| Leaks at the screws, dry elsewhere | Lid flexes between screws, or squeeze too low | Add screws, stiffen the lid, raise the squeeze a few percent |
| Weeping straight through the gasket | Gaps between lines or layers | Dry the filament, print slower, add perimeters, check for under-extrusion |
| Seals at first, leaks after days or heat | Compression set | Lower the squeeze if the gasket is overstressed, use a harder grade, move it away from heat |
| Gasket slips out of the groove | Groove too wide or too shallow | Narrow the groove, or add a lip that sits in a second small groove |
| Cracks or tears at inside corners | Sharp corners | Add fillets, thicken the section |
| Blobs and strings on the sealing face | Wet filament or too hot | Dry the spool, lower the nozzle about 5 °C |
Common mistakes and where to go next
- Treating a printed gasket as certified for fuel, pressure or food contact.
- Choosing the softest grade because it seals best on paper, then fighting jams. Start at 95A and move down.
- Over-squeezing to stop a leak. Going past the rubber guideline of about 30% mostly shortens life; fix flatness or screw spacing instead.
- Ignoring the first layer. It is the sealing face on the bed side, so a rough or lifted first layer will leak. Getting a TPU part off the sheet without damage is covered in TPU bed adhesion.
- Picking the material by label alone. TPU vs TPE explains how to compare flexible grades, and functional household prints covers design rules for other everyday parts.
Frequently asked questions
What Shore hardness is best for a 3D printed gasket?
Start with 95A because it feeds reliably, then move to 85A if your fasteners cannot supply enough force. Parker’s handbook calls 70–80 Shore A the best compromise for rubber seals, but printable TPU is mostly 85A and harder; Bambu Lab, for example, does not support anything softer than 85A on its printers.
How much should a TPU gasket be compressed?
Parker gives about 30% as the static maximum for rubber O-rings and says the squeeze should never be below about 0.2 mm. For printed TPU we suggest starting at 10–20% and testing, since no published figure exists for hobby filament. A hard stop around the groove keeps the squeeze consistent.
Are 3D printed TPU gaskets waterproof?
Not by default. Water can pass between lines and layers, and Prusa’s watertight guide needs extra perimeters and flow even for rigid filaments. Print with solid perimeters, dry filament and a proper groove, then test with water before you trust it.
Can I print a TPU O-ring?
You can print a ring, but the round cross-section of a true O-ring prints poorly on a flat bed. A rectangular or chamfered section in a groove is easier to print and compress. Printed rings are not suited to fuel, high pressure or high temperature; use moulded rubber there.
Sources
- Parker O-Ring Handbook (squeeze, gland fill, stretch, hardness; written for rubber O-rings; copy hosted by University of Arizona)
- Stratasys: FDM TPU 92A data sheet (compression set, applications)
- Polymaker: PolyFlex TPU95 technical data
- Prusa Knowledge Base: Watertight prints
- Prusa Knowledge Base: Flexible materials
- NinjaTek: Printing guidelines
- NinjaTek: NinjaFlex technical specifications (PDF)
- Recreus: Filaflex 82A printing parameters
- Bambu Lab Wiki: TPU printing guide
