Found this via Twitter:
http://www.backcountry.com/therm-a-rest ... ad#reviews
Tab down to a review titled 'Science Lesson'
About twice I have noticed mine go partially down - one was last winter in minus temperatures.
Neoair - the science
Moderators: Bearbonesnorm, Taylor, Chew
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Blackhound
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Bearbonesnorm
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Re: Neoair - the science
Every air mat I've used regardless of make, always seems to lose some pressure during the night ... I just thought they were 'self leveling' 
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