Is the raw stuff we devour - plastic, steel, concrete, energy - going down even as the economy grows?

Imagine that every year, every one of us gave birth to an eight-year-old made from steel. Disturbing image.

Now go further. Imagine that you also gave birth - everyone, male and female, young and old, every year - to 10 cement, one plastic and three paper eight-year-olds and one new-born aluminium baby.

Well, in a sense, you do. This is the global average production per head of stuff: about 200kg (441lb) of steel each, for example, enough to sculpt a child.

But we aren't all at the global average. In the UK, our annual consumption of materials is about three times higher.

So for the UK, we're not talking about a family of eight-year-olds any more, we're talking about enough raw materials to create adults.

This is just a visualisation of the amount of stuff we produce, no more, and if you find it odd, no problem. But for some, it might just make resource use more meaningful.

The aluminium baby is now a year or two old and the others have grown up and multiplied, as you can see. Welcome to the stuff family you might never have known you had, reborn every year.

Don't be confused by steel producing fewer people than paper despite weighing more. It's because steel is more dense so you can sculpt less from it.

The top line of the graphic features some extra stuff people in black. That's because creating all the other material people requires energy equivalent to burning about 12 parents.

The idea for the image - a variation on the idea of the resource footprint - comes from Dr Julian Allwood and colleagues at Cambridge University, including his PhD students.

The calculation is rough and ready, and I come to slightly lower numbers than Allwood and co, but the point is that this measurement uses a unit we're familiar with - us.

They have just finished several years of research on primary materials - what we'll call stuff - and put it in a book, Sustainable Materials With Both Eyes Open, free to download and fascinating for umpteen reasons.

Here are just two. First, the style of the argument. Instead of the usual ya-boo about sustainability, this is a pragmatic guide to getting more value from less stuff. Researched with long-term co-operation from industry, it emphasises facts and evidence but is aimed at a popular readership.

"My PhD students were nervous and surprised at the first draft, says Allwood. "They were imagining something much like a journal paper. But there's not much point. It wouldn't have any effect. We're all learning to engage."

Go Figure would award Nobel prizes for rigorous popularisation. The brilliant trend-setter was Dave MacKay's free book Sustainable Energy Without the Hot Air.

That said, the second point is the sustainability argument itself. For all the ingenuity of the image, are you surprised by the size of your stuff family? Is it a fair way of showing the data? We count population in millions and billions, but human flesh and blood is still a small part of the world. And so by comparing material-size to people-size, are we measuring primary material consumption on the right scale? Either way, it sure makes you think.

Your stuff family grew from not much above zero in a little over 100 years

Not least because, as the authors point out, your stuff family grew from not much above zero in a little over 100 years. The materials age began in earnest only at about the turn of the 20th Century.

Is that growth sustainable? As it happens, some think we've just passed the point of peak stuff, as it's been called, and that the annually-reborn stuff family has begun to shrink.

Chris Goodall, an environmental writer, recently argued that economic growth has run alongside a reduction in our consumption of stuff. Might growth even have driven that decline, he asks?

He has a strong case that resource use has not kept pace with GDP growth. But has it actually done better still and fallen? That's harder to say.

Taking any particular material, it's hard to know if the UK has reduced its consumption of that stuff, changed from one kind of stuff to a new kind of stuff, or simply moved the manufacture of it elsewhere in the world while still buying it in. Just because many of the numbers have gone down, doesn't prove the thesis.

Probably the best available figures are for flows of total materials. Here's Goodall's own data for this measure of total stuff, measured in millions of tonnes, derived from the UK environmental accounts.

Goodall looks at this graph and says that it more or less levels off throughout the UK's boom years of the 1990s and 2000s - despite soaring GDP - and that it was already on a downward path before the latest recession kicked in.

What do you think?

If we put a linear trendline on the data, the claim that we're flat or on the way down looks debateable, though you could also draw different kinds of trendline.

But this trendline does expose the peaks and troughs caused by economic boom and bust. It's easier now to appreciate that what looks like a period of flatness might be the effect of using a starting point at the peak of the late-80s economic boom - just as we might say that the flatness from the 70s to the mid 80s was the result of the early 80s recession.

We have to strip out these ups and downs to understand the underlying trend. When we do, well, you decide - has it really levelled off or fallen?

Either way, I would applaud serious questions of this kind, even as I would wonder about the conclusions.

If the stuff problem is improving, all well and good, but I don't think the case is proven. Somehow, I suspect there'll be a big demand for all the thinking we can muster about how to make the most of the materials we have, whether for profit or sustainability.