How to Eco Product Design

Carbon footprint (CO2e) refers to all greenhouse gases including methane and nitrous oxide.

We were asked to design a bird feeder that could be easily washed to remove the damp seeds left in the bottom of the feeder. ​We wanted to make it out of plastic so it would be easy to clean and cheap to mould, but is this good for the environment?
bird feeder-sketch
bird feeder sketch

We decided to use Polypropylene (PP) for the coloured parts with an ultraviolet additive to stop the colour fading in the sun.  Polycarbonate (PC) was used for the clear parts because it’s optically clear, durable, scratch resistant  and hard wearing.  although PP and PC can be recycled are incinerated or go to landfill because they are not collected by the council.

The sketches shown above were approved by the client and then we develop the idea in CAD.

The factory that moulded the parts was next door to the client so the transport footprint was low. The cost to manufacture in the UK was lower than China as long as the automated moulding machine was run for 24 hours to produce 5000 sets of parts in one run.

The clear plastic body was made in 2 halves joined together by ultrasonic welding. No screws  or chemicals were needed. The wall sections were kept thin while still maintaining their strength. It is easy and intuitive to fill the birdfeeder with seeds and hang up on a hook or branch.

bird feeder image
bird feeder product
bird feeder

By using a free emission factor database at  we found that Polypropylene  creates 4.4kg of CO2e per kg of plastic injection mouldings. We duplicated this by the weight of PP used per bird feeder. 4.4 x 0.07 = 0.3kg CO2e
We also found that Polycarbonate was 7.6 kg or CO2e per kg of plastic injection mouldings. We duplicated this by the weight of PC in each bird feeder. 7.6 x 0.18 = 1.37kgCO2e
The total CO2e emissions per feeder was 1.67kg CO2e. This doesn’t include the packaging and transport emissions, and end of life emmisions.

bird feeder CAD

A CAD programme called SolidWorks  has a Life Cycle Assessment feature called Solidworks Sustainability.

We imported the parts into Solidworks to evaluate the carbon footprint of the assembly more accurately. We choose the material and production method  from the database. We selected Polypropylene for the coloured parts. We selected Acrylic (PMMA) instead of Polycarbonate  for the clear body because it had a lower carbon footprint. It was optically clear, hardwearing and recyclable. We selected the region of the world where the parts would be made and sold.  We specified the type of transport used and life expectancy of the product. We specified the end off life disposal; landfill, incineration or recycling. The sustainability calculator estimated a total of 1 kg CO2e would be emitted per bird feeder.  This was lower than our rough estimate above.

The non renewable energy used would be 18MJ. The amount of air acidification which makes acid rain would be 0.0032 kg SO2e. The amount of water eutrophication (damaging nutrients added to water) would be 0.0004kg PO4e.

This Life Cycle assessment was then saved as a benchmark so we could modify the dimensions, materials and manufacturing methods to see if we could reduce the environmental damage.

Solidworks Sustainability can also estimate the environmental impact of electronic circuit boards. Just select circuit board as a part material. It can also calculate the impact of energy used to wash the birdfeeder with warm water each month; although we didn’t do this.

We then designed a ceramic bird feeder made of natural materials to see if it would have a lower footprint and appeal to an eco conscious consumer.
bird feeder sketch

We use Sketchbook Pro to sketch up our ideas.    Sketchbook Pro only costs £16.74. It’s a pleasure to use and makes your sketches look better. You’ll need a stylus pen and a Cintiq  monitor connected to your PC or Mac. Once you have a side view sketch you can import this on a sketch plane within the CAD package to  trace over.


We imported the sketch into Solidworks and made a 3D CAD model so we could ran the Solidworks Sustainability life cycle assessment to see if it was better or worse for the environment.

3d cad model
3d cad

The sustainability calculator estimated a total of 1.3 kg CO2e would be emitted per ceramic bird feeder.  Surprisingly this was higher than the plastic bird feeder made from petroleum based plastics.

The non renewable energy used would be lower at 12MJ. The amount of air acidification which makes acid rain would be more at 0.0058 kg So2e. The amount of water eutrophication (damaging nutrients added to water) would be more at 0.0008 kg PO4e. ​

We then CAD model a metal bird feeder to see how that would compare.


The sustainability calculator estimated the painted steel bird feeder would cause 0.6 kg CO2e; about half of the plastic bird feeder.

The non renewable energy used would be lower at 7.5MJ. The amount air acidification would be much less at 0.0015 kg So2e. The amount of water eutrophication would be a lot less at 0.00026 kg PO4e.

Finally we made a CAD model of an wooden bird feeder.

bambo bird feeder

The sustainability calculator estimated the bambo bird feeder would cause 0.53 kg CO2e; less than all the other designs.

The non renewable energy used would be lower at 4.3MJ. The amount air acidification would be  000.51 kg So2e. The amount of water eutrophication would be 0.00034 kg PO4e.

We wanted to see of using recycled plastic would be better option but the Solidworks sustainability database didn’t  have recycled Polypropylene or recycled acrylic as an option so we had to estimate these. Companies report saving over 50% of CO2e emissions by using 100% recycled plastic.
100% recycled PET is available from recycled clear plastic bottles which could replace the acrylic body and tray. 100% recycled black Polypropylene is also available but we needed green so couldn’t use that option. By using recycled PET for the clear body and tray we estimate it would save about 25%  CO2e per bird feeder.

Another option is to use Bio Based polypropylene made from organic matter. The bioplastics calculator on the Natureworks website estimated a 60% reduction of CO2e when using Biobased plastics similar to PP and PC.

CO2e emissions

The plastic bird feeder made from bio based plastics had the lowest CO2e emissions.

The plastic design has a clear body so we can see when it’s empty and needs cleaning. It’s easy to refill and is more hygienic when washed. If the bird feeder is washed in warm water regularly this would also add to CO2e emissions over it’s 10 year life. In the instructions it should explain using warm water instead of hot water saves CO2e emmisions.

There is a free LCA program called open LCA and material databases available but are difficult to use. If a client wants a more bespoke LCA then they would need to ask a professional LCA consultant for help.

Is a bird feeder a useful product to have during a climate emergency? Yes because many birds would die without the help of bird feeders because their natural habitat has been reduced in cities. People love watching the birds feeding which is good. Planting bushes and trees with berries on and leaving plant heads on over winter help birds feed naturally.

In a climate emergency we want to reduce CO2e emissions ASAP. Consumers should live within their personal carbon allowance of less than 9.5 tons per year during 2022.  If they can buy and maintain a birdfeeder within their allowance then this is OK.