Some distinctions are necessary for the issue not to be treated as an either/or.

1
Certainly, for many powered products, incremental improvements in efficiency mean that longer lasting products limit the 
uptake of more efficient versions. Where rates of these improvements can be predicted, it is fairly straightforward 
mathematical problem to work out the rate at which products should be replaced, on the basis of whole of life cycle 
assessments (with appropriately determined functional unit). Nicola Morelli did some strong work in this area with 
reference to Australia; more current European work in the context of Extended Producer Responsibility is being done at 
the moment by Tim Cooper.

Where product efficiency improvements demand product replacement, industry should be (made) responsible for product 
take-back, component recovery (as incremental efficiency improvements by definition do not require entire systems to be 
redesigned), material recovery (mechanically processed), and only after all these alternatives have been undertaken, 
material recycling (chemically processed). This has long been the argument of Walter Stahel.

Pro-free marketeers have long defended product obsolescence (or rather, sacrificing research and design investment and 
so final product capital costs, in the name of speed-to-market, cheapness-of-product balanced against brand-equity, 
and the inability of consumers to adequately calculate whole-of-life running costs) as a driver of innovation, an 
economically determinist argument with a techno-utopian warrant. If there is any merit to the argument, manufacturers 
(and designers) should back it up by designing infrastructures for product take-back.

2
Product-use-lives depend on their make-up but also their use. Designers have tended to think about design for product-
life-extension as a materials selection issue, rather than as a design-of-use issue. This has been because designers tend 
to believe that people want products that as maintenance-free as possible (something currently being contested by 'slow' 
and DIY movements).

 There is historical evidence that maintenance-freer material durability in use always comes at a cost up or down-stream 
of the life cycle (as with asbestos). Longer lasting materials generally need more energy input in extraction and 
processing and manufacturing, and/or in post-use-life material extraction, recovery and disposal. Sometimes, this 
increased energy input is needed to negotiate compounds or chemicals that are toxic in manufacturing and disposal. 
Again, life cycle assessment calculations have long attempted to calculate optimum solutions, with more success in 
relation to embodied- energy/use-life ratios than in relation to eco-impacting manufacturing and disposal (how to rate 
this toxicity versus that one, or a material produced in a country with strict regulations in relation to that toxin versus the 
same material produced in a country without such environmentally management manufacturing/disposal). Schmidt-Bleek 
and Wuppertal Institut have long conducted Materials Intensity Per unit Service (MIPS) analyses, which take account of 
ecological rucksacks (the weight of material used in the whole life cycle, as compared to the final material weight of 
product, pro rata per functional unit or use-life).

For product use-life extension, if the energy is not put into the material up-front, it generally needs to be put into the 
material during its use-life, via maintenance and repair – oiling or painting timber, keeping materials dry and dust free, 
replacing shortest life components without replacing the whole product, etc.

3
Current research in sustainable design is focused on product-service-systems, and not just cleaner production eco-
efficient product design. Product-service systems aims to facilitate 

a) increased product use intensity or productivity (expert help or professional use), 

b) product-life extension (maintenance, repair)

c) product take-back and remanufacturing (leasing, pooling)
In other words, product-service systems aim to provide maintenance rather than expect it of the material. Generally 
product-service systems aim to be businesses that internalise the whole-of-life costs of products, because businesses 
are better at being economically rational (and so sustainable) than consumers/users (that target of sustainable 
consumption moralising). However, there are also many not-for-profit, non-marketised, community-based sustainable 
product-service systems, particularly in the expert help, maintenance, repair area. See Manzini's EMUDE project.

4
As always, Manzini has provided the most useful rules-of-thumb (though see also the EcoDesign Foundation's work on 
sustainments):
A) Match material life with product life, supplemented by appropriate product management, roughly divided into three
> eternal products (heirlooms, monuments) > 30 years – with maintenance
> medium-life products (5-30 years) – with repair, upgrade and take-back
> short-term products < 5 years – made-from materials that plentiful, renewable, and recoverable in low energy ways 
(recyclable, biodegradable)
The classic misalignment is plastic, an amazing, and amazingly durable material which through semiotic quirks of the 
20th Century (see Miekle) is now mostly used in shorter term products (packaging, toys, gimmicks).

B) Design for error-friendliness (or what Fiskel calls system resilience) — i.e., choose reversible strategies and design the 
reversing that might be needed.

For Tim Cooper, see: http://extra.shu.ac.uk/productlife/
On EcoDesign Foundation and sustainments in relation to the above, see Tony Fry and Anne-Marie Willis' now on-line 
history of steel: http://www.teamdes.com.au/steelbook.html
J. Fiksel, “Designing Resilient, Sustainable Systems,” Environmental Science & Technology, Dec. 2003
Rutgers University Press (November 1997)
E.Manzini "Prometheus of the Everyday: The Ecology of the Artificial and the Designer's Responsibility" Design Issues, Vol. 
9, No. 1 (Autumn, 1992)
Ezio Manzini The Material of Invention: Materials and Design Cambridge MIT 1989
Meikle, J. American Plastic: A Cultural History Rutgers University Press (November 1997)
Morelli, N. (2001) ‘Technological Innovation and Resource Efficiency. A Model for Australian Household Appliances’ 
Journal of Sustainable Product Design, Kuwler Publisher, Amsterdam, pp 3-17.
MIPS. A universal ecological measure?. 
Schmidt-Bleek, F Fresenius Environmental Bulletin. Vol. 2, no. 6, pp. 306-311. 1993
Stahel, Walter. 1994. “The Utilization-Focused Service Economy: Resource Efficiency and Product-Life Extension,” in 
Allenby and Richards, Greening of Industrial Ecosystems, National Academy of Engineering, Washington DC,. Available 
through the National Academy Press Office (202-334-3313)

Cameron