AskPablo: Glass vs. PET Bottles

PET.jpgChris McLaren, owner of Lush Beverages of Ottawa, Canada, sent this week’s question. He changed his packaging from glass to PET this year, partially for environmental reasons. But to date no one has been able to quantify those reasons for him. I will give it the old Boy Scout try to see if I can substantiate his decision numbers.

Here is what we know:

  • The bottles contain 12 fl. oz. (355 ml)

  • 12 fl. oz. weighs 355 g (1 ml of water weighs 1 g)
  • An empty glass bottle weighs 250-280 g ( we will use 265 g)
  • An empty PET bottle weighs 28-32 g (we will use 30 g)
  • PET bottles are always made from virgin materials and never recycled into new bottles
  • Transportation distance is hard to estimate since there are many points of sale

It is difficult for a company to know what happens with their packaging after the product leaves their facility. We can encourage consumers to reuse and recycle but ultimately it is out of our control. This is why I encourage companies that I work with to minimize the ecological impact of their packing production since that is something that they do have control over. And this is exactly what Chris is trying to do. Clif Bar did this by making their foil wrappers thinner, probably saving tons of polypropylene plastic each year.
Reducing packaging weight is also a great way to save on shipping costs. Chris tells me that, due to the lightness of the PET bottles, he is able to get 72 cases on a standard 48″ x 48″ pallet, instead of the 60 cases with glass bottles. This not only increases the amount of product per truckload but also economizes on fuel use.
The semi trucks used to transport Chris’ product probably get around 6.1 mpg (2.6 km/l) and can carry up to 45,000 pounds (20,412 kg). Over 260 km the truck would use 100 liters of diesel fuel, emitting 301 kg of CO2 (for a derivation of this see “AskPablo: The Tailpipe Mystery”). Transport emissions are often based on units of tkm (weight transported x distance). In this case we are looking at 301 kg of CO2 emissions and 5307.12 tkm (20.412 t x 260 km), or 56.7 g/tkm. The Wuppertal Institute’s MIPS Data Tables actually put the figure at 102.00 g/tkm, but that is for an “8 t articulated lorry” in Europe.
Before we look any more into transportation let’s look at the material intensity of making the bottle. Material intensity is a measure of all material inputs related to product outputs and provides a measure of material use efficiency. Glass uses 3.04 g/g of abiotic materials (minerals and fossil fuels), 17.1 g/g of water, and emits 0.716 g/g of GHGs. PET uses 6.45 g/g of abiotic materials (minerals and fossil fuels), 294.2 g/g of water, and emits 3.723 g/g of GHGs. The material intensity, in terms of gram per gram, is great for PET but keep in mind that the PET bottle also weighs quite a bit less. Next we will see how that factors in.
By multiplying the weight of the empty PET bottle by the material intensity factors we determine that one bottle represents 193.5 g of abiotic material (mainly oil), 8826 g of water (mainly in power-plant cooling water), and 11.7 g of GHGs. The glass bottle is almost nine times as heavy at 265 g and is responsible for 805.6 g of abiotic material (mainly sand and oil), 4532 g of water (again, from power-plant cooling water), and 189.7 g of GHGs (that’s about 15x more than the plastic bottle).
Focusing more on the GHG emissions, let’s look at trucking emissions. Each bottle contains the same amount of product, 355 g, but the glass bottle weigh 335 g more than the PET bottles. To find out how much GHGs that is over 1000 km we first calculate our tkm (335 g x 1000 km = 0.335 tkm) and multiply it by the trucking emission factor from earlier (56.7 g/tkm) to get 18.99 g (0.335 tkm x 56.7 g/tkm). So, each PET bottle that is shipped 1000 km saves 19 g of CO2 over the equivalent glass bottle, that is 456 g per case, or 19 tons per million bottles. Now that is just the difference between the two bottles, but what is the total GHG impact for 1000 bottles?
One thousand PET bottles represent 11.7 kg of GHG emissions for manufacture. Once filled, they collectively weigh 385 kg (385 g x 1000). When shipped 1000 km this equals 385 tkm (0.385 t x 1000 km), which equals 21.83 kg of CO2 (385 tkm x 56.7 g/tkm). This adds up to 33.5 kg (11.7 kg + 21.83 kg) of CO2 for every 1000 PET bottles shipped 1000 km. Compare this with 224.9 kg for 1000 glass bottles shipped 1000 miles, and these calculations don’t even take into account the delivery of the bottles from the bottle factory, which would add a few more kg.
Chris, consider your decision justified and thank you for Asking Pablo!
Pablo Päster, MBA
Sustainability Engineer
View Pablo Paster's profile on LinkedIn

21 responses

  1. I think a more fundamental question to ask in this instance is what is in these bottles and why do we need to buy it. You are using the weight of water in your calculations to work out how much the bottles weigh when full — there is no reason why we need to be buying bottled water. What is wrong with the stuff that comes out of the tap? It creates no excess packaging waste, incurs minimal transportation expenses… I could go on but surely we’ve all heard this before…

  2. Hi Jessica,

    I am the manufacturer of the product discussed in this week’s column. The product is an alcoholic cooler: carbonated, with 20% juice, 7% vodka, and natural flavours and colours.

    I suspect that Pablo chose to use the density of water in his calculations as it is a very easy figure to work with, and the density of most beverages (including mine) are very close to this figure.

    I myself do not manufacturer (or purchase, for that matter) bottled water, a practice which I would agree with you is highly wasteful. In my particular case I believe the complexity of my product warrants packaging.

    I can tell you that all ingredients are sourced as close to the manufacturing site as possible. Water is on-site, commodity ingredients are typically on-site in bulk, juices are shipped in concentrates, and vodka is shipped as 96% pure ethanol: all of this minimizes freight. This is generally the practice across the beverage industry.

    I would consider larger unit sizes to reduce the ratio of package vs. liquid by volume, save for two reasons: a)
    the alcohol market (people in bars & restaurants) demand traditional single-serving sizes, and b) carbonated beverages need to be consumed shortly after opening.

    In the future, I would like to move from PET to emerging biodegradable plastics such as PLA (polylactic acid). I would certainly pay a premium as a manufacturer, if any, to do this. I expect in the future the cost will weigh in favour of PLA. The problem right now with these emerging plastics is that they are not always suitable for certain ingredients (alcohol, acids, etc), and I understand they have a short shelf life. Still, they hold a lot of promise.

    I hope this helps a bit. If you have any other questions or comments, feel free to contact me directly. Thanks!

  3. Well, for refillable bottles: from what I understand, PET bottles are never refilled. Perhaps because PET bottles are damaged easily: once they are empty, they collapse quite easily (because they are so thin). I suspect it would be impossible to get a reasonable percentage of undamaged bottles (or any, for that matter) back to the filling site. In addition to appearance quality, there also seems to be technical issues: I know that PET bottles are recycled to fibers, and not new PET bottles. For some reason, ‘virgin’ PET is required for beverage bottles. (Not sure the exact reasons). Finally, the collection system (even for glass other than beer) is simply not in place, and this would require action at a much higher level than where I am sitting.
    Some good news is that the liquor boards in Canada are collecting deposits on all bottles, including PET, to attempt to drive recycling percentages much higher.
    From my perspective, I think the best way I could contribute to solving this problem (without closing up shop, of course.. :) is to try to move to biodegradable plastics as soon as technically feasible. I don’t think any other option is practical (or even plausible) for me.
    Another point you might be interested in: In Ottawa, like many Canadian municipalities, we have organics/compost collection. I inquired with the city about six months ago with regards to their support for biodegradable plastics in the compost stream. At the time, I had thought these degradable plastics might be feasible and was thinking about labeling the bottles as ‘compostable’.
    I received this response: “For the reasons discussed, Ottawa would be reluctant to accept biodegradable bottles in an organics program, until greater public awareness is evident. This move will require extensive effort from municipalities and industry to attain.”
    In the full context, I must agree with the city on this one: the main argument being the public is easily confused (no offence to my neighbours..) But it is better to have biodegradable plastics in landfill than non-biodegradable PET accidentally being put into the compost stream.
    So it comes down to consumer education: industry and government promoting the use of biodegradables. Maybe I’m 2 years too soon, and need to wait for some of the technical issues to be solved, but right now it doesn’t look like there is much activity on the marketing side.

  4. Not to completely change the shift of this discussion away from bottles, but I agree completely about the problem of consumer education with regard to new types of plastic. My copy of “An Inconvenient Truth” came wrapped in plastic bearing a sticker informing me that it was compost-able, but I have not seen any other similar labels on plastics I have encountered.
    I can take plastics with 2 and 4 recycling codes to my local recycling centre, but many plastics, films in particular, don’t bear any code, and I am left guessing.
    With the introduction of biodegradable and compost-able plastics, we definitely need some way of teaching consumers that not all plastics are alike…

  5. Hi How many times do i need to refill / recycle a litre glass bottle, with water at home…For it to compensate GHGs produced during making etc when compared to buying the same water volume in plastic or pet bottles from a store?

  6. Dear Pablo,
    While doing research on the PET bottles, I found this very interesting post of yours on the glass vs. PET bottles. Your conclusion was “This adds up to 33.5 kg (11.7 kg + 21.83 kg) of CO2 for every 1000 PET bottles shipped 1000 km.” So 33.5 grams per bottle transported 1000 km?
    I am researching on a technology that converts plastics back into fuel. It would take 55 of the PET bottles (or 1.842 kg of CO2) in your example to generate 1 liter of gasoline. Since this liter of gasoline is not using any “new” crude oil but is simply extracted from waste plastic that would have only added to the non-biodegradable mess at the city dump, what kind of “carbon neutrality” (or carbon positive impact) is achieved by this process? I don’t know if the environmental impact of the lesser load on the city dump can be measured, but what about each liter of gasoline generated from recycled plastic instead of freshly extracted crude oil? How does that lessen the CO2 impact?
    I am not a member of any of the lists you regularly write on, but would you be kind enough to respond to me at this e-mail ID?
    Thanks in advance and keep up the good work!
    Parag Raval

  7. Chris, you noted that
    “For some reason, ‘virgin’ PET is required for beverage bottles. (Not sure the exact reasons).”
    Mainly because health authorities (US-FDA, etc.) regulating the placing of beverage products on the market have resisted authorizing it until they can be assured that the tech exists to provide high-quality recycled PET that does introduce contaminants into the beverage. Such tech has been around for several years, but only recently have the health authorities been willing to entertain changing their regulations on “materials and article in contact with food” to reflect the current state-of-the-art.
    Keith R

  8. When I was a boy I bought soda, etc. from machines in glass bottles and right next to the machine was a crate to place your empty bottle. There was no deposit return, we just turned them in. When my mother bought milk, Juice, and soda at the grocery store they were in glass bottles and we returned them when we went to the grocery again. These bottles were washed, sterilized and reused. It was neat to get a really old bottle from time to time as a kid. The logos etc were painted on the glass, not wrapped on the bottle with paper or plastics. This was the 1980s in the US. It worked very well, it was efficient, clean, and I imagine more energy efficient and cheaper. Also, it occurs to me that sense glass bottles with metal caps are not penetrated by air etc. as plastics are that the shelf life and quality of the products was probably higher. It also occurs to me that at that time a glass bottle of coca cola was $.50 then and if you apply 3% inflation over lets say 25 years then it should cost about $1.05 now, but in every machine I can find now a plastic coca cola cost $1.25. We are filling land fills, arguably saving little to no energy, and saving no money.
    Tell me again how are these plastic bottles better than reusing glass bottles.
    Maybe I am missing something.

  9. I believe your calculations for g/g GHG for PET emissions are very wrong. When you say it’s 15x more for a plastic bottle, that is based on your incorrect calculations – 30 x 3.723 is not in fact 11.7 but 111.7. This then follows through your calculations, and should be 133.5kg total not 33.5kg. It still proves your point, but less so.

  10. This is a terrific topic and I think you have done an excellent job of analyzing this issue from the transportation and storage end.
    Nobody is going to argue that plastics are lighter and smaller and that transportation energy will be saved by going with plastics.
    However, what about:
    1) the recycle-ability of plastic vs glass?
    -Can all plastic be recycled? can all glass be?
    -What is the reality of recycling for the two?
    2) the amount of pollution from production of the different containers?
    -Which process creates more contaminants?
    3) the amount of energy needed for production of the different containers?
    -Which process takes more energy?
    4) of those container that are NOT recycled, what is the difference in environmental impact?
    My point is that there are many facets of the glass vs plastic debate, I hope folks don’t pick a “winner” based solely on the transportation & storage argument that was initially presented.

  11. We seem to be unreasonably biased:
    – Against plastics,
    – For biodegradable materials
    – For the technology of yesteryears.
    What is it we want to achieve? Lower GHG emissions? Lower use of nonrenewable resources? Less volume in landfills? Lower pollution of ground waters or air? Something else?
    Glass containers use a lot of energy and generate a lot of GHG (see discussions above). Then we have to take into account that return bottles require washing and sterilization, hence energy for hot water and chemicals. Also the disposal of the dirty water is part of the equation. The bottles last for about 20 return trips, what happens to them afterwards?
    Biodegradable materials make sense only if they are composted at the end. If they are land filled they rot quite slowly generating potent GHG (methane) and require sealing the landfill site to prevent contamination of ground water by leachate. That further slows the decomposition process. The landfills are unstable for many years. Biodegradable plastics exist (polylactates) but they have to be separated for composting, else we would contaminate the compost by other plastics.
    Plastics are light, and except in some instances are superior to all other options. Some are recycled (PET bottles) and it does not make difference that they are converted to fibres where they replace virgin resin. The energy in plastics can easily be recovered by burning and producing electricity and heat. Also when buried they cannot contaminate air or groundwater.
    My feeling is that plastics should be the materials of choice. However, the local conditions are important: Is there a composting facility? Do we collect and use the landfill off gases? Is there an incinerator and is it used for generating energy? And so forth.
    One thing though puzzles me: Most of the GHG are generated by burning fossil fuels in our SUVs and our oversize homes, most of the landfill space is taken by paper, like the fliers we discard without reading. Should not we address these issues with the same vigor?

  12. dear ,
    in my country there is a 19 liters drinking water delivery,some bottles are made from polycarbonated plastics and other from pet…
    please can you reply telling me which kind of plastic can be refilled by the bottling factory and for how many times? and why?
    thanks in advance….

  13. Glass 100% recyclable and reusable. Plastic bottles reusable but seriously how many plastic bottle can one reused before having too much that they have to be thrown out. Plastics have many issues, i.e. chemicals that may be harmful like gender altering hormones. Plastic bottles are more convenient but maybe that is a bad thing. So maybe we consume less soda since its a bit more inconvenient to carry around. Isn’t that better for us healthwise? Plastics, when it come to packaging food, is usually the worst solution for the environment and personally.

  14. Dear Pablo
    we would like to fill beer in mono layer pet bottle ,please let us know have you any idea for sterilization or pasteurizer filled beer bottle.

  15. This discussion so far has mostly ignored the large amount of petroleum used to make glass because of the high melting point of silica.

  16. I have spent all day researching the carbon footprint of bottles vs. other packaging, and this was the most concise.
    Do you know anyone who has done a good job on the Carbon footprint of Bag-in-box?

  17. Hello
    It is nice about this discussion,I am looking for Comparison of Glass bottles vs PET vs Aluminium Bottles vs Tetra pak.. can anyone please help me on this particular topic. i am working on a project regarding this. Please help me out

  18. I even wonder, when i take my glass bottles round to the recycling center by car, it uses perhaps 1 liter of fuel.

    A PET bottle, is normally thrown in the bin, and probably ends up at an incinerator. Since the bottles are basically Hyrdogen, carbon and oxygen, they probably provide excellent fuel for the incinerator.

    On the other hand, a glass bottle thrown into the bin, and ending up in the incinerator would probably create bottom ash, and mix with the other toxic metals.

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