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Environmental Analysis of Cloth Diapering

Are cloth diapers better for the environment than disposables?  

Cloth diapers are often held up as the greener alternative to disposable diapers, and while some parents choose cloth primarily for baby reasons, others choose cloth mostly for the environmental reasons.  Do some googling, though, and you are going to find a universe of conflicting information on the environmental performance of cloth v. disposable diapers.  So what gives?  Are cloth diapers really greener than disposables?

We didn’t feel fully qualified to give a scientific answer to this question ourselves, but fortunately we have a close relationship with the principals at Point380, a Boulder-based environmental consulting firm that specializes in carbon and energy management and strategy.  They agreed to look in-depth at the issues and so we asked them to write this section and to be available to answer questions on our blog, too.  They have performed similar analyses for major international food & beverage manufactures, biodiesel refiners, developers, electric utilities, publishers, refineries, etc., so we think they can handle this one. 

Warning: this section is long and, we assume for most people, as boring as all get-out.  But as far as we know, it is the most thorough examination of the issues you are going to find from a cloth diaper service.

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Cloth diapers and disposable diapers in an environmental perspective: the “short” version

In terms of environmental issues, the most important points of comparison between cloth diapers and disposables are:

  • Raw materials

  • Water use

  • Life-cycle energy use (and consequently, greenhouse gas emissions)

  • Disposal

  • Uncontained post-use environmental contamination

A full list would be much longer, but these five points encapsulate the majority of the impacts of diapering.

There have been multiple Life Cycle Assessments (LCA) of diapering systems, but the most recent, thorough and unbiased LCA was performed by the UK Environment Office (link to study).  While we have some reservations and quibbles with their analysis, it is clearly the most legitimate study to date and our comparison is based primarily off their study. 

The most important assumption in any comparison like this is the number of diapers used in each system.  The UK study used a 2.5-year “diaper life” (length of time that an average child would be in diapers full time) and from there estimated that roughly 4,000 disposables or about 5,000 cotton diapers would be used in 2.5 years (preliminary surveys showed that parents using cotton diapers change their children more often; this data has not been well confirmed).  Crucial to the comparison as well is how many individual cotton diapers are actually used in 2.5 years, for the point of using reusable diapers is that they are reused.  From Bundle’s and the UK LCA numbers, we assume this number is roughly 60 (a single diaper can be reused roughly 100 times).

Raw materials:  Disposable diapers are mostly cellulose pulp derived from trees (40%), Super Absorbent Polymer (SAP) derived from crude oil (30%), and plastic derived from crude oil (25%).  Cotton diapers are generally 100% cotton.  The proper comparison here is 4,000 disposables vs. 60 cotton diapers, and reusable diapers clearly win in this category.   On a # of diapers consumed basis, disposables use roughly 180 kg of processed resources while cotton diapers use roughly 4 kg of cotton lint.

Water use:  The comparison here is between water used in the manufacturing of ~4,000 disposable diapers vs. the water used in growing 60 cotton diapers, plus the water used in washing ~5,000 cotton diapers.  For cloth diapers, it turns out that the majority of the water use is in the growing of the cotton, not in the washing, which is highly efficient in using only about ¼ - ½ gallon of water per diaper, per wash load.  Overall, though, disposables use less water than cotton diapers.

Energy use: The proper comparison is between life-cycle energy for disposables (growing, raw material processing, plastics and SAP manufacture, diaper manufacture, transport, disposal) and life-cycle energy for reusable cloth (growing and processing, diaper production, laundering, transport).  Note that for reusable cloth diapers, the life-cycle comparison should be broken out between growing and manufacture of diapers (60 total)  and laundering and transport (5,000 total). The UK study results showed disposables as coming out with slightly lower energy use and GHG emissions than cloth diapers.  We feel that this component of the UK LCA study has the largest sources of potential error (in other words, we believe the results are preliminary at best and the error bars are larger than the differences).  Of particular concern is how the study accounts for methane (CH4), a potent greenhouse gas.  The study shows disposables responsible for 3 times the amount of methane as reusable diapers.  The global warming potential of this difference is greater than the difference in life-cycle carbon dioxide (CO2) between the two systems, so any slight change in the relative ratio of methane between the two systems will affect which system emits fewer greenhouse gasses.

Disposal: The vast majority of disposables in the U.S. are disposed of in landfills and 4,000 disposable diapers generate roughly 2,000 lbs (1 ton) of solid waste.  Bundle sells its retired cotton diapers as rags to other commercial and industrial users and a reasonable assumption is that most are used to extinction (meaning used indefinitely until they disintegrate and thus not landfilled).  For disposables, sealed landfills significantly slow degradation of the solid waste.  Further, disposables are effectively plastic-sealed by the body of the diaper and the common plastic trash can liner.  It is likely that disposables will remain in landfill for 500-1,000 years before degrading.  Cloth diapers are clearly superior in this category.

Uncontained environmental contamination:  The question here is whether the solid and liquid wastes in disposables escape the landfill and whether the effluent from washing the cloth diapers escapes into surface water.  The answer is largely “no” in both cases.  Modern U.S. landfills are tightly regulated by the EPA and are well contained.   Bundle’s washing machine effluent is dumped to the local sewage treatment system, which is highly treated before being re-injected into the subsurface (treatment of municipal sewage is also tightly regulated by the EPA).  Neither diapering system likely contributes to post-use uncontained environmental contamination.

Conclusions

Weighting the five categories considered above by importance to the environment is a bit arbitrary and depends on an individual’s priorities.  In two categories (raw materials and disposal), cotton diapers are clearly superior.  In two other categories (energy/greenhouse gasses and post-use contamination) the two systems are roughly equal.  The only category in which disposables are superior to cloth diapers is in water use. 

Water use as an environmental concern must be carefully considered in context, however. It should first be noted that most of the water use in question is not local water use but is used where the cotton is grown (Asia).  Secondly, the term water “consumption” is used quite loosely by many people.  In fact, water is part of the hydrological cycle, in which it rains and collects on the surface, evaporates back into the air, and then rains again, in a continuous global cycle.  Water used by the citizens of a municipality is “consumed” in the sense that it is shunted to the sewage system after use, but in fact the water is cleaned and returned either to ground or surface water, where it returns to the hydrological cycle.  Similarly, water “consumed” by cotton plants actually evapotranspirates back into the atmosphere, where it is once again part of the hydrological cycle.  The real concern with water is with water shortages for communities.  Areas with severe water shortages should carefully consider how their water is being used.  Despite some popular perception, Boulder (where the diapers are laundered) is not in water crisis.

On the balance, we feel that reusable cloth diapers are superior in environmental performance to disposables.  Of the categories considered above, if we were to rank the environmental effects by their relative impacts, we see the solid waste disposal question as by far the most important, raw and processed resource use the next (both favoring cloth), then water (favoring disposables), energy and finally post-use environmental contamination (both favoring neither choice).

Note that this analysis should be considered the “short answer” or the executive summary to a much larger body of work.   A longer analysis will be posted here in pdf when it is available.