Price

Temperature

Mechanical Strength
Stress Tolerance

Friction

Food Safety

Environmental
Tolerances

Environmental
concerns

The cost of material is often a key consideration by many. Certainly nobody wishes to pay a greater price than necessary. But when used to compare vendors, price alone may not be inappropriate, as other factors will nearly always influence the cost in an upward direction.
PLA is certainly the least expensive material, Nylon the most expensive.
But, a key consideration is just how much material is to be used on the project, as to whether the material cost is a going to be significant determining factor.

For comparison, a 10 mm model (1000 cubic mm) might use 10 grams of material. A 20 mm model will use 8000 cubic mm, and thus weigh 8 times as much : 80 grams. The cost of the material (PLA) around 4 cents per gram, so 10 mm version will cost $0.40, the 20 mm version $3.20. In Nylon at around 15 cents per gram, the cost of 10 mm model $1.50, the 20 mm model $12.00
the 20 mm model will take more time to print, the printing time likely to be also 8 times longer. If a 10 mm model takes 30 minutes to print, the 20 mm version likely around 240 minutes. If, At $5 per hour, the 10 mm model costs $2.50 in printer time, the 20 mm model costs around $20.

The above analysis is just for purpose of illustration, and should not be used for price comparison, as other factors also come into play in determining the final cost.

The printing time is determined largely by the shape and size of the model, and it will be roughly the same no matter what material is used. Note that the effect of supports if required will change this perspective somewhat, as the time taken to print the supports may be much greater than printing the model itself.
Conclusion:
The cost of the material used forms a small part of the cost. The lower cost material may not meet all of your requirements. We suggest is that its wise to select the material used based on its fitness to purpose, and not just the cost.

Different plastic materials soften and melt at different temperatures. The temperatures generally much lower than metal and wood. But the plastics can often stand in place of metals in terms of strength requirements. We must pay attention to the range of temperatures that the model will experience when put into service to ensure that it remains sufficiently strong when it reaches the highest expected temperature. The general term used is called “temperature tolerance”.
When a model is printed, a temperature of > 200 C is used to fully melt the material allowing it to be formed into shape. When the model is cooled, then (broadly speaking) the model will be subject to environmental temperature in the range 0C to 50C.
PLA Plastic starts to become soft at around 55C. Polycarbonate on the other hand, starts to soften at around 147C. Other materials somewhere in between.
So, what temperatures can be expected in typical situations?:

1. Room temperature: 20 - 25 C (30 - 40 C on a hot day)

2. Exposed to the sun i.e. Car Dashboard: 100C +

3. Inside the engine bay of a car: 100C ++ (water cooled engine)

4. Dishwasher: 66 - 74 C

5. Industrial machinery: 40-150C (or more)

Conclusion: Temperature tolerance is often a key requirement in determining the type of material best suited to an application.

The mechanical strength of material is a big topic and highly technical, hard to cover it well in this short summary.
Broadly, you want the printed model to be able to withstand the stresses applied to it when installed. You also need to understand how the material will behave when the applied stress is greater than its permanent breaking point. Does it “shatter” into a thousand pieces, or does it just bend gracefully ?. When the stress is removed, does the object restore its shape or is it permanently deformed. ?
What is the nature of the stress applied to the printed part ? Is it compressive or tension ? Is it a bending stress ? Is it a shear stress ? What about friction (see below) ?
FDM Printed models are printed in lines that have a directional factor in regards strength. The term used is “anisotropic”. The model is strongest in the X-Y orientation when printing. When strength is a required characteristic, careful attention must be paid to the orientation of the model when compared to the stress applied to the model when installed.

For comparison, the term “Isotropic” means “same in all directions”, “Anisotropic” means “not the same in all directions”, the opposite.

The strength of the model is largely informed by the adhesion of one printed layer to adjacent layers (aove, below and alongside). The strength itself determined by material properties of self-adhesion, when a line of hot semi-liquid plastic is laid on top of another solidified line. The various plastics differ in this characteristic. The strength of a particular material is given by the manufacturer, in the form of a Technical Data Sheet when the material is used under standardised controlled conditions and stresses are applied in standard ways.

It may seem surprising, but not every plastic filament manufacturer supplies such information. The fact that they do or do not is read as understood to be an indicator of material quality. We at Tech3DPrint select materials from manufacturers that supply both TDS and SDS (Safety Data Sheets) for all of their material. Certainly, the generation of the TDS and SDS is an added cost to the manufacturer, and its reflected in the price of their products.

So, selection of a material will include a consideration of the physical stresses that the model must endure. It may not always be practicable to measure the stresses, but in a product development situation, different materials may be tested, and the one selected is one having lowest cost with sufficient strength to endure the stresses. If we have no idea on the level of the stresses, its tempting to just pick the highest strength material available and hope for the best. But a better choice can be made if the stresses are understood and the most appropriate material selected. This will ultimately lead to a printed model that lasts longer.

FDM printed models will always have layer lines. When one object moves against another, the friction will be least when applied in the same direction as the layer lines, and greatest when applied across the lines. The material itself has a coefficient of friction, and its different across various materials.

When the amount of friction is important, then we consider the materials having an lower friction coefficient. Nylon (with no additives) is a low friction material. Essentium HTN is an example of Nylon formulated to have very low friction. But when material such as Carbon os Glass fibre is added, the level of friction will increase. POM material has extremely low friction, but it is truly difficult to print with FDM techniques, due to its high coefficient of expansion/contraction leading to a strong tendency to warp or deform during printing. ABS Plastic with infused Kevlar or ABS with Polycarbonate copolymer have lower friction, and easier to print. The low friction materials tend to be higher cost.

Its pretty common to see requests for models where food safety is a factor. Anything coming contact with food falls into this category.
The first part of the consideration is the material itself, as to whether it contains poisons that may harm human or animal health. The second part is what happens to food safety when the material is printed with FDM techniques.
So, in regards the first part, most FDM printable materials are generally safe when sourced from reputable manufacturers. There are some exclusions of course. Those that have the greatest food safe formulation will be those having a US FDA classification of “Food Safe” or “Food Contact”. Polypropylene is an example of such material.
In regards the second part is the problematic area. When FDM printed, the plastic model will have microscopic pores/cavities, and the layer lines of course. Both provide opportunities for microscopic organisms to lodge and propagate. The organisms may or may not be safe to human and animal health. The model might be washed in a dishwasher, and the high temperatures are designed to sterilise the object and kill most bacteria. The plastic material may be tolerant of dishwasher temperatures, but this may not be sufficient to kill dangerous organisms including viruses.
The pathway to achieving a food safe FDM printed product is to seal the surface of the product after printing to close up the microscopic pores and crevices in layer lines. A smoothing solvent may be applied to the model, or a sealing spray may be applied, which of itself must be food safe. To be considered safe, Solvents must evaporate completely, leaving no residue.
All of this will leave a residual liability risk on the product manufacturer should things go wrong despite all diligent efforts. Most FDM printers are small business concerns, and not necessarily insured or capitalised to take on projects involving high risk. Some may ask customers to sign a disclaimer absolving the manufacturer of liability, but it’s unclear if such documents carry legal weight.
Most FDM printing businesses will not be insured against such risk, and in any case one must consider whether any insurance coverage would be adequate if a negative event involving human health or morbidity were to occur. Nobody would wish to be to culpable for causing ill health to another, and it would cause anguish and heartache for most.
If the techniques to make the product food safe are in accord with industry best practice and insurance coverage is adequate, then the project could go ahead and the residual effect will be an increase in cost due to the increased use of time, materials and the insurance cost. It’s important for customers to be aware of the issues in this area.

Finally, a pathway to produce food safe moulds does exist, for models used to make cookies and similar food products: FDM Printing can be used to make a mould for the making of (pourable) silicone moulds. Silicone material is generally regarded as food safe. Obviously this would cost a little more than simply printing of a cookie cutter, with two stages required. The technique of mould making using FDM printing is an area requiring study before I can say more on this topic.

Beside Temperature (see above) there are other environmental factors that need to be considered. In particular, when the printed model is to be exposed to environmental factors that might affect its lifetime. These factors include: UV Light and Water Exposure.

UV Tolerance

UV Light can cause some plastics to degrade. It may be fading of colours, or it may go as far as degradation of the material itself. Of course the different polymers behave differently under the stress of UV exposure. New Zealand may be highly exposed to the thread of UV exposure, due to the Ozone Hole located in the southern hemisphere. Whilst measures were put in place in 1989to reduce man made degradation of the Ozone Layer, its clear that the degradation remains. Thus, when a printed model is to be subjected to outside exposure, its tolerance to UV radiation must be a consideration. In particular, ASA material is regarded as the best UV tolerant material, others such as Polycarbonate (with UV stabiliser) also have some level of tolerance.

Water Tolerance

Some plastics will degrade when exposed for long periods in water, particularly sea water. Its due to adsorption of the water into the pores of the material. Water resistant materials include ASA, ABS, Nylon 12 (PA 12), and PETG.

Microorganism Tolerance

Various microorganisms such as Fungi, Bacteria and Algae can degrade plastics over time. Indeed, when plastics are not degradable in this way there is an environmental concern as this leads to issues when the plastic is disposed of. But in particular applications measures can be taken to reduce breakdown. An example is PLA infused with Copper, which can be used when algae growth would degrade functionality of the plastic part.

All plastics have some level of environmental concern when they are disposed in waste in an uncontrolled way. Some plastics, such as PLA degrade in the environment naturally, others contain additives like PFAS that actively prevent such degradation.
The ready degradability of PLA can only be realised under industrial waste handling conditions. It’s not degradable enough just to safely dispose of in landfill. In general, 3d printed plastic products need to be disposed by incineration to be considered environmentally safe.
PFAS chemicals are a class of chemicals used to make products grease proof, water-proof, stick-proof, and stain-resistant. They are added to: Food Packaging: pizza boxes, food wrappers, take out containers, microwave popcorn bags, disposable trays, and bakery bags; Non-stick pans (Teflon).

When the person ordering a 3D printed product has a concern for the environment, they would select a material such as PLA that more readily degrades. Sometimes that just is not possible due to conflicting requirements. In such cases, the product needs to be responsibly disposed by incineration when it reaches the end of its life. Some materials can be recycled, others not so much. Recycling is only possible when the material is known. At Tech3dprint, we identify the material used to the customer. The customer may also request that appropriate symbols be imprinted onto the model allowing it to be identified when it comes time to be disposed. This would allow recyclable materials to be identified with appropriate disposal pathway chosen at the time.