The Thingiverse is already full of great food-contacting objects, from shot glasses to forks, and the list is bound to grow as more MakerBot-wielding college students move back to their dorms and discover, late at night, that they are out of clean dishes… But before you set out to fab yourself a new table setting, it’s important to know a little bit about what materials may or may not be food safe, and what you can do to make them safer.

Before we start, keep in mind that, though I have a decent amount of experience in designing children’s toys, and consumer products, I wouldn’t call myself an expert on food-material interaction. I’ll be linking to outside information, but be extra-careful with anything you might make. I’ll cover some “risk factors” at the end of the post, and hopefully that will help you to be better informed makers. OK. Legal spiel over.

First, what does “food safe” mean anyway? To put it simply, “food safe” or “food grade” is a distinction determined by your country’s food control organization. In the United States, that’s the FDA, which publishes its regulations concerning plastics which contact food in CFR Title 21 — be prepared for some heavy stuff. Sheesh. In Europe or the UK, the regulatory agencies are different, and have different standards, but more on that later. At the most basic, these regulations try to nail down three things:

1. How “Virgin” is the plastic? Virgin plastic is made from 100% raw petroleum, natural gas, or other feedstocks. This means it has had the least chance to be contaminated with anything. Non-virgin plastic can be of a few types. Pre-consumer recycled (sometimes called “regrind) plastics are made using at least some plastic that had already been made into a product, but for whatever reason, didn’t leave the factory. Maybe Stonyfield farms misprinted a bunch of strawberry yogurt cups. Rather than just throw them out (and probably because they can’t regrind them themselves, because of the ink used in printing) they sell them to Recycline. They mix the reground cups with some virgin plastic (for strength) and mold them into toothbrushes. So, from this example, we can see that pre-consumer regrind is somewhat more contaminated (with ink, lubricants and glues) which makes it less suitable for touching-food applications. But it can touch your mouth in a toothbrush. Keeping the example moving, maybe you buy a toothbrush, and use it for 3 months. Recycline lets you send it back to them to be recycled again. At this point, it is post-consumer regrind, which makes it very unlikely to meet the standards for food safety, since the manufacturer literally doesn’t know where it has been. So, it’s generally made into things like plastic lumber, or fibers for fleece(in the case of soda bottles). Every regrinding and reheating makes the plastic weaker too, so these last two products don’t need much strength or purity.
2. What does the plastic have in it? Though plastic is generally a pretty simple Monomer (like styrene), Homopolymer (like Delrin), or Copolymer (like ABS), manufacturers like to add little proprietary “improvements” in the form of catalysts, plasticizers, flame retardants, colorants, and protectants (like UV blockers). These components are never listed on products, so it’s important that somebody check that no overtly toxic chemicals are in your soup bowl. However, regulations to not preclude the use of toxic chemicals, especially those which have not been tested for toxicity in low doses. For example, antimony dioxide is generally used as a catalyst to speed up the polymerization of PET plastics used in soda bottles. The chemical remains in the plastic, and can leach out into water or food stored in it, but it is allowed by the FDAs regulations.
3. How accurately mixed and polymerized is the plastic? Plastic is a mixture, and if its mix is off in any way, it can be more susceptible to leaching that excess material into food. Imagine pancake batter with too much milk. If you let it sit, it will tend to separate into batter on the bottom, and milk on the top — milk that is like an unreacted constituent of a plastic. Plastic is also the result of a chemical reaction, which can be more or less finished. If the plastic hasn’t polymerized completely (in the case of epoxies, especially) then it can be liable to leach unreacted components into food. This basically guards the consumer against low-quality grades of plastic in food situations.

So, you can see that regulations don’t necessarily do much for us, in terms of real-world food safety. There are a number of disadvantages we have. We are taking an existing plastic, and re-melting it, and re-extruding it, which may alter its chemistry by re-heating. We may not have complete control over the admixture of our plastic — the extra chemicals that make it more flexible, cheaper, or flame resistant — so we can’t really check the interaction of those chemicals.

Most importantly, even the FDA’s regulations don’t necessarily protect us from toxins in plastics. The antimony debate is still going on, but the FDA has responded that the levels of leaching are below the limits established by the EPA for clean water. Another example of regulations doing more confusing than assisting were the recent eruptions of outrage over phthalates in PVC and BPA in polycarbonates. These additives are used to make the plastics they are a part of more flexible, and are an important part of making PC and PVC usable plastics. Moreover, they are not acutely toxic (like snake venom, or lead, which hurt you quickly). Instead the accumulate in body fat, where they act as hormone disruptors, potentially causing cancer and developmental defects throughout life. Because studies had not confirmed these effects until recently, regulations allowed for even large amounts of these chemicals to be used (BPA is still used in many polycarbonate and epoxy food industrial food containers, and PVC is still used in some cling wraps). In contrast, the EU, and UK are much more stringent in their restriction of chemicals which even show the potential of being harmful, and therefore have much more stringent controls on food safe plastic types.

But if you can’t trust the regulations, and you can’t necessarily rely on the manufacturers, what can you do? In this case, you’re best bet is to find out as much as you can about your options, and then apply these rules, where possible:

1. Avoid: high temperatures, acid foods, alcohol, and oil, or strong detergent contact. All of these can break down or partially dissolve the surface of plastics, letting chemicals they contain out into your food.
2. Dry food, cold liquid, or food that minimizes contact (like salad, or chips) are apt to interact less with the object that hold them, and leach less from them.
3. Use plastics like ABS, Polystyrene, Polyethelene, Acetal (Delrin), and Nylon, which are listed by the manufacturer as food safe. These plastics have longer histories of study, since they are older, and also generally use additives less frequently.
4. Avoid, especially for DIY projects: Epoxy (except explicitly food grade), Polycarbonate, Polyvinyl Chloride (PVC). Also steers clear of plastics which have high flexibility or elasticity, which can be more porous than hard plastics.
5. If you notice a plastic staining when it contacts food, like spaghetti sauce, or becoming milky instead of clear, don’t use it. These are signs that the food is seeping into the plastic, which means the plastic could be seeping into the food.
6. If you can, coat the unsafe part with a safe coating. Hard waxes like carnauba or resins like shellac can be used to coat objects which will not need to bend. If bending is desirable, food-grade silicone or epoxy sealants may be used, with the caveat that you can only trust them as far as they are regulated — carnauba and shellac have been literally eaten for thousands of years without issue.

But probably the most important thing you can do is remember that any material that isn’t totally inert will leach chemicals. The bet way to be safe is to use tried and tested materials. Wood, Glass, and Stainless steel are probably best for long-term use. So let’s set our sights on those options in the long term (how cool would a wood making MakerBot be?!), and just be as careful as possible in the short term.

Be safe out there, fabrigourmands, and if you have any other tips to share, get on the comment train!