What makes a material or product “green?” This is one of the most frequently posed questions in the building construction industry today and it exemplifies the shift towards sustainable priorities in architecture. But this inherently straightforward question leads to anything but a simple answer. When a well-meaning client or student asks, “What makes it green?” the design professional will inevitably deliver this sensible yet unsatisfying response: “It depends.” However, the inherent complexities and unresolved issues that characterize the emerging field of sustainable materials should not thwart our thoughtful attempts to provide more definitive answers.

On the positive side, we now have access to a clearer, more developed picture about the effects of particular materials on environmental health. Over the past 50 years, significant pieces of environmental legislation and “green” economic instruments have dramatically transformed the fields of manufacturing and construction. Also, from Rachel Carson’s Silent Spring to the 2001 Stockholm Convention treaty, landmark publications have promulgated convincing arguments for the avoidance of particular substances. New so-called material black lists, such as the Restriction of Hazardous Substances Directive, are composed of the worst offenders for human and environmental healthvolatile organic compounds (VOCs), such as benzene and carbon tetrachloride, join toxic materials, such as asbestos and cyanide, to formulate a picture of the part of the material spectrum that is clearly not green.

While these black lists are well-established and defensible (although still growing), composing a comparable “green list” is more complicated. Obviously, we can look to naturally occurring substances that pose no health risks and which safely decay at the end of their useful life without burdening the waste stream or polluting the environment. Consider Mycobond, a biocomposite that uses mycelium, the vegetative part of a fungus such as a mushroom, in conjunction with aggregates such as rice hulls, cotton burrs, and buckwheat hulls, to create composites that can be used in board insulation and packaging. Green Island, N.Y.–based Ecovative Design is using this material in its EcoCradle packaging, which was recently adopted by furniture manufacturer Steelcase. Ideally, the biological nutrients sourced for products would be rapidly renewable, would require minimal energy investment in their harvesting and processing, and could eventually be transformed into high-quality feedstock for future materials. However, we know that materials are inherently contextual and should not be studied in a vacuum. Even the most environmentally friendly material can cause environmental damage if it promotes the disruption of existing ecosystems or requires energy-intensive transportation for its distribution. (This is the reason that I decided to include general environmental attributes as opposed to a quantifiable green rating system in my Transmaterial series because what makes a material green is not limited to its own physical properties.)

Difficulties aside, the understandable desire for answers has led to the rapidly growing field of environmental standards and eco-labeling. Entities such as the International Organization for Standardization, the American National Standards Institute, and ASTM International have all developed environmental standards, although compliance is voluntary and the organizations do not certify products. The desire for product certification—combined with the recognized commercial value of green productshas led to an explosion of new environmental programs, green rating systems, and eco-labels. Organizations such as the Forest Stewardship Council and the Carpet and Rug Institute have provided helpful guidance concerning the responsible selection of particular products, but the sheer number and variety of new programs has overwhelmed the building industry. In addition, the authenticity and rigor of a particular program’s certification process is not always obvious, and the lure of potential profits has led many companies to make nebulous or unverifiable environmental claimsaka “greenwashing.” Another difficult challenge in environmental product certification is proprietary information. Most companies do not wish to disclose their particular product recipes and processing techniques, so comprehensive and well-informed eco-labeling is likely to remain difficult.

Naturally, architects and designers cannot wait for the establishment of complete and reliable product certification in order to specify materials for their projects; nor should they follow green labels blindly without leaving room for critical thinking and innovation. Even if comprehensive eco-labeling were attainable, certification is only part of the story. Design professionals must consider materials within their broader ecological contexts, appraising their life cycles and anticipated energy and resource exchanges. After all, materials are not fixed entities but part of a flow that defines the continual construction and deconstruction of the built environment. As Stewart Brand states in his influential book How Buildings Learn: What Happens After They’re Built, architecture should not be defined as “the art of building,” but rather as “the design-science of the life of buildings.” It is only by assessing this expansive spatiotemporal scale that we may begin to determine better environmental strategies—and ultimately what makes greener materials.

Blaine Brownell is a Minnesota-based architect, author, materials researcher, and sustainable building adviser. His weekly product e-mails and Transmaterial books profile materials that are redefining our physical environment.