Thursday, August 31, 2006

12 Layers of Newspaper

Attached are some additional results on the insulation properties of newspaper! This follows a suggestion by Tony in the green building forum.

12 layers of old newspaper were lightly crumpled and sealed together with tape and then used to encase a carton box. The overall thickness of the combined newspaper layers was between 10mm (base) and 20mm (side). This was similar to the multifoil dimensions. The carton box, and its contents were identical to that described in the previous posting. The only difference between this and previous experiments was a slightly higher external temperature of 23C. The experiment was run for approximately 6 hours.

In addition I also repeated the experiment with 2 layers of aluminium foil to provide a reflective barrier either side of the 12 layers of newspapers.

The results are summarised in the attached graphs. The insulation properties of 12 layers of paper are not surprisingly better than the carton box alone, but slightly worse than the multifoil. However, by placing one layer of aluminium foil on the inside and another on the outside of the newspaper, the insulation properties were identical to the multifoil material.

Figure 4a shows the temperature time data plotted on the same graph as in the previous posting. To facilitate comparison Fig 4b shows the same curves without the datapoints, but normalised to a common start temperature and start time. This provides a simple visual comparison of all the experiments and clearly illustrates how multifoil insulation is a very expensive alternative to newspaper and kitchen foil!

For those who are still not convinced the data is linearised in fig6a by plotting log(T-Te). The slope of the multifoil and the newspaper + foil are, within experimental error, identical.

Why should only 2 layers of foil have the equivalent effect of the 12 layers used in multifoil? The answer I believe is simple. The 10 inner layers of foil have no insulation properties, all the reflective effects are produced by the outside layers. There is absolutely no insulating benefit of having them there at all. On the contrary, the inner layers could well reduce the insulating properties of the foil. Since aluminium is such a good conductor the inner layers will conduct the heat away to the nearest cold junction (a compressed edge, a join or hole) rather than reflect it back 'through' the first layer.

Given the cost of waste newspaper (free to a good home) it would make a very interesting costbenefit analysis and no doubt an extremely good business case - also not a bad use of recycled paper.