Evaluating outdoor gear with open source hardware

In an academic publication, this space would be filled with justifications of the physical, mental and social benefits of outdoor activities and the importance of its associated clothing; this audience will be intrinsically aware of these benefits and keenly aware of the importance of good clothing for enjoyment, comfort and safety in the outdoors.

But what exactly does 'good clothing mean? In addition to effective design, fit, and aesthetics, probably the most important measurable properties of clothing are thermal and evaporative resistance. Thermal resistance might also be referred to as thermal insulation, or (a little incorrectly) - "how warm" something is to wear. Evaporative resistance is usually called 'breathability' or sometimes 'water vapour transmission'. Apart from factors beyond your control (primarily ambient temperature), evaporative resistance is the main factor deciding how much moisture condenses in your clothing system and how much can escape.

Thermal resistance is a particularly useful property to measure, because empirically-derived models exist which allow you to use metabolic rate (exercise intensity) and ambient conditions (temperature, wind speed, radiant temperature etc) to estimate what thermal resistance is required.

The quantitative measurement of these clothing properties is also crucial for quality control (e.g. for companies sourcing products from new manufacturers) and for product development (i.e. is the new Mk II product better than the Mk I). Although manufacturers often have good data regarding their products, consumers are usually bombarded with confusing information, skewed by industry-bias and marketing hype.

Thermal and evaporative resistance measurements are typically made by universities and research institutions. Thermal manikins and other devices have been used for many decades to measure the thermal resistance (insulation) or evaporative resistance (breathability) of clothing. The first thermal manikins were probably those used by the US military in the early 1940s - at a time when many troops were lost to cold rather than bullets. An interesting history of manikins can be found 202006/2nd%20publish%20Proceeding_all-in-one%5b061005%5drev02.pdf">here, written by Dr Ralph Goldman.

Online publications like backpackinglight.com, and their associated communities, seek to provide unbiased information which is more useful to consumers, and have developed quite sophisticated equipment with which to do this (see articles by Roger Caffin and Jerry Adams).

In this article the potential of relatively recent developments in open source hardware (specifically the Arduino platform) in developing equipment to quantitatively evaluate outdoor clothing will be explored. An example of a thermal manikin developed at a fraction of the cost of commercial equipment will be presented, and suggestions for future developments discussed. My aim is simply to share what I know with the people that are mostly likely to find this information useful. I hope it complements the work already presented on backpackinglight.com.

ARTICLE OUTLINE

• Introduction
• Development of a thermal manikin
  • Principal of operation
  • Introduction to Arduino
  • First two prototypes
  • "Working prototype"
  • Electronics
  • Temperature sensors
  • Climate chamber
  • Other limitations and scope for improvement
• Case studies
• Conclusions
• Further resources

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