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2017-01-02

Wearable air conditioning? Passively cooling the human body with nanoPE


The era of global warming creates days when virtually any textile cover may appear too much. That is because all garments heat, even if that effect depends on the type and thickness of used filaments. A new, low-cost material developed at Stanford by the research group of Yi Cui has now developed passive cooling as a breakthrough method of thermal management. It might even result in large energy savings by reducing expenses for air conditioning. Their fabric, nanoPE (nanoporous polyethylene) textile may be thought of as an enhancement on the theme of saran wrap. It consists of two layers of intransparent and nanoporous polyethylene film interspersed with a layer of cotton mesh for strength and thickness. It virtually does not reflect infrared radiation emitted by the human body, producing a cooling effect unavailable with conventional fabric.  It is also permeable to water vapor, which makes it an effective and scalable textile for personal thermal management. What is not entirely clear yet is how nanoPE behaves under UV radiation, in heavy use, and after multiple laundry cycles.

The polyethylene material, already commonly used in battery manufacturing, has a particular nanostructure with pores that measure 50 to 1,000 nm in diameter – a spacing that allows the passage of the body’s infrared radiation yet causes sunlight to scatter and reflect upon contact with its surface. The nanoPE fabric reflected 99% of visible light, contrary to commercially available polyethylene that let 80% of visible light pass through. The resulting skin surface temperature was 3.6oF (2.7oC) lower than under ordinary cotton fabric.

Because few studies looked into engineering the radiation characteristics of textiles, this research would appear to open new avenues to passive temperature management without involving outside energy sources, merely by tuning materials so as to dissipate or trap infrared radiation.

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