Eco Bricks, why their weight is important.

As EcoBricks are becoming more popular many people will start to make them, eagerly stuffing their waste plastic into bottles… but wait, there’s a catch, a stumbling block, a trip hazard that many people fall victim to when making their very first brick. After a few days of bottle stuffing they proudly hold their first brick before them. Ready to add their brick to the Eco Brick registry they take a photograph (even a brick selfie)  of their brick and start to enter the details, but they get stung when asked what the weight of their brick is. To their horror. they’re told that their brick does not meet the minimum requirements. It gets rejected by the Eco Brick moderators and they’re left with a useless plastic bottle filled with plastic.

What? I have to weigh my brick??? Why?

The reason many people fail on their first Eco Brick is due to the weight of the brick. I’m going to tell you why the weight of an Eco Brick is so important. It’s all about strength and load capacity.


the capacity of an object or substance to withstand great force or pressure.

I’m going to focus this post on why the weight of an Eco Brick is so important. The main reason for making an Eco Brick is to turn plastic waste that cannot be recycled into something USEABLE. A useable and recyclable building block that can withstand the elements, being sat on, built with, built upon and be used as a seat, a wall, a door, a table… there are so many possibilities for building with Eco Bricks but the brick itself MUST be up to the challenge. A brick that is not full enough and packed enough will not have the correct density to withstand these building challenges. Worst case scenario is that the brick splits, spilling its contents and failing the structure it is part of. Best case scenario is that the bottle just buckles under pressure and needs to be replaced.

To find a perfect weight for your bottle you need to do some maths.

Take the bottle’s volume in millilitres, so a 1L bottle will be 1,000ml. Times this by 0.33 and you will get the minimum density for that bottle. Note I say MINIMUM, this is the very bottom of the scale for density, ideally you’d want the bottle to be a little way over that. So the maths again:

V(volume) X 0.3 = minimum density

So a 1L bottle would need to weigh at least 330g to be dense enough, ideally somewhere around the 350g mark would be perfect. To achieve this weight the plastic contained within would need to be cut up into small pieces and packed really really tightly. When you see 330g of plastic waste in a carrier bag it will look like it would never fit into a 1L bottle, but believe me with some decent scissors, a metal stick and ten minutes of your time you’ll get it all in.

To help you on getting the correct density of your Eco Brick, I’ve put together this table which shows the conversions between bottle volume and weight.
For Full Size image ecobrickweightguide

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