Quick3D Typical vs minimum values on a datasheet
Why most 3D-printing datasheets give typical values, how they differ from minimum values, what ± means, and why you still need a safety factor.
Most numbers on a 3D-printing datasheet are typical values. That single word changes how you should use them. This article explains what typical, minimum and ± values mean, and how to turn them into a design you can trust.
Key takeaways
- Most datasheet numbers are typical values: averages, with results above and below.
- Typical values are for comparing materials; minimum values are better for design.
- Printed parts scatter more than moulded ones, and brands test differently.
- Use the weakest relevant direction, add a safety factor and test real parts.
Typical values
A typical value is a representative result, usually the average of a set of test specimens. If a lab tests ten tensile bars, the typical strength sits near the middle of those ten results. Some bars broke above it. Some broke below it.
Typical values are the right tool for comparing materials. They are the wrong tool for proving a part will not fail, because a real part can land anywhere in the scatter, and often below it once you add real-world geometry and print settings.
Minimum and specification values
A minimum or specification value is a lower bound that the manufacturer commits to. Batches are tested, and material that falls below the limit should not ship. These values are lower than typical ones, sometimes noticeably so, because they have to cover the weak end of normal production.
Minimum values are common for raw engineering plastics and metals sold against a specification. They are rare on 3D-printing datasheets. When you do see them, they are far more useful for design. In fields like aerospace, engineers go further and use statistically derived design allowables based on many tests across several batches.
Typical value
A representative average. Use it to compare and shortlist materials.
Minimum value
A lower bound the maker commits to. Far more useful for design.
Reading ± values
Some sheets add a ± figure after a value. Most often this is one standard deviation: a measure of how spread out the results were. Occasionally it shows the full spread from lowest to highest. The sheet rarely says which, so treat it as a hint about consistency rather than a strict band.
Under a normal distribution, about two thirds of results fall within one standard deviation of the average. That means roughly one specimen in six comes in below “average minus one standard deviation”. A small ± is a good sign: the material and the test were consistent. A large one tells you to expect more variation in your parts.
Why scatter is bigger for printed parts
Moulded plastic specimens are quite repeatable. Printed ones add new sources of variation:
- Layer adhesion, which depends on temperature, speed and cooling.
- Small voids between extruded lines or within sintered powder.
- Moisture in the filament or powder.
- Cure depth and post-cure for resins.
- Machine-to-machine differences, even with identical settings.
So even a carefully measured typical value carries more uncertainty for a print than for a moulding.
Scatter across brands
Different brands of the same polymer do not report the same number either. Formulation, test standard and specimen preparation all vary. For example, PETG materials in our catalog report tensile strengths of 17.9–105 MPa (median 50 MPa, 30 materials). That spread is partly real differences between grades and partly differences in how each brand tested. See comparing materials across brands.
- Formfutura 928.6–100
- Polymaker 836.1–100.3
- Fiberlogy 717.9–105
- 3DXTECH 347–56
Bar = lowest to highest, dot = median. 27 materials, live from our database.
Good to know
Each bar mixes plain, blended and filled grades tested in different ways. A wider bar does not mean a less consistent brand.
Why you add a safety factor
A safety factor is the margin between the load you expect and the load the part should be able to carry. You divide a material value by it to get a working value. It covers everything the datasheet does not:
- The gap between typical and worst-case material.
- Weaker directions in the print, especially across layers.
- Stress concentrations at holes, corners and threads.
- Heat, which lowers strength and stiffness.
- Creep: plastics slowly deform under a constant load.
- Fatigue: repeated loads cause failure well below the static strength.
- Ageing from UV, moisture and chemicals.
- Loads you did not anticipate.
Watch out
There is no universal number. The right factor depends on how well you know the loads, how bad a failure would be, and whether any industry code applies. Parts carrying sustained, repeated or impact loads, or parts where failure could hurt someone, need a much larger margin and proper testing. If in doubt, ask an engineer who can take responsibility for the design.
Questions to ask about any value
Before you rely on a number, run through these questions. The answers are usually in the footnotes or the test method column.
- Is it typical, minimum or a range? If the sheet does not say, assume typical.
- How many specimens? A value from five bars is less certain than one from fifty. Few sheets say, but some do.
- One batch or many? Batch-to-batch variation is not captured by a single test series.
- Which direction? A printed value usually refers to the strongest orientation unless stated.
- Which condition? Dry or conditioned, annealed or as printed, fully cured or not.
If you need firmer numbers for a critical part, ask the supplier whether lot-specific test data or a certificate of analysis is available. Some industrial grades offer this; most hobby-grade materials do not.
Typical values still have a job
None of this makes typical values useless. They are the fairest way to rank materials against each other, as long as the test conditions match. They tell you roughly where a material sits in its family and whether it is worth testing. The mistake is only in treating them as guaranteed design numbers.
A practical approach
- Use typical values to build a shortlist.
- Prefer the value for the weakest relevant direction, such as Z for FFF parts. See print orientation.
- Apply a safety factor that matches the risk.
- Print real parts, or test coupons, with your actual settings, and test them.
- Keep the print settings fixed once a part passes.
For the bigger picture, start with how to read a TDS.
See PETG values across brands 34 materials