Forum Index > Gear Talk > Pad deflating, or barometer rising?
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Luc
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Luc
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PostTue Aug 02, 2022 5:32 pm 
Is atmospheric pressure change overnight something that could be significant enough to make one think their pad has a leak? Asking for a friend.

GNGSTR
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dave allyn
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PostWed Aug 03, 2022 6:53 am 
Good question. My thermarest mattress seems to lose a small amount of air overnight. I've tried running it through a tub of water, couldn't find so much as a bubble. Tried spraying water and dish soap on it (the soap makes the bubbles from the air). No sign of a leak. Doesn't lose enough that I can feel the ground.

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Bernardo
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PostThu Aug 04, 2022 2:13 am 
I have this happen as well. Maybe the pressure created by body weight plays a role?

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texasbb
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PostThu Aug 04, 2022 7:04 am 
Temperature.

thunderhead, Cyclopath
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pula58
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PostThu Aug 04, 2022 9:36 am 
If you inflate your pad with air at a certain temperature (ambient air temp, and/or your exhaled breath that is warm), when the air temp lowers at night (and/or the ground is cold-snow for example) the air volume inside the pad decreases (PV=nRT). It's physics. I suspect that many sleeping pad reviews that complain about leaks might not be leaks at all.

thunderhead
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Brockton
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PostThu Aug 04, 2022 11:26 pm 
I'm pretty sure I've experienced slight decrease in pad pressure as it cools off over the course of the night.

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Cyclopath
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PostFri Aug 05, 2022 11:03 am 
texasbb wrote:
Temperature.
Did you inflate the pad by mouth by any chance, or with some kind of pump? The air gets colder overnight even if you use a pump but if you're exhaling into it that air has been warmed by your body.

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Cyclopath
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PostFri Aug 05, 2022 11:04 am 
Also, of you have a Garmin watch, you can check the barometric pressure history at any time. smile.gif To rule theories in or out.

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neek
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PostFri Aug 05, 2022 11:24 am 
Cyclopath wrote:
The air gets colder overnight even if you use a pump but if you're exhaling into it that air has been warmed by your body.
However, one needs to account for the fact that some people blow more hot air than others. Note the reverse can happen too. I returned to the tent one hot afternoon last week to find my pad about ready to explode.

Chief Joseph
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Luc
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Luc
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PostFri Aug 05, 2022 6:46 pm 
Mystery solved! I've also noticed my pad getting firmer after a hot day hiking from basecamp. I guess one thing I (I mean my friend) has noticed is when rambling around in the truck with my bed still setup in the back, the pad clearly changes pressure as the elevation changes.

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texasbb
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PostSat Aug 06, 2022 9:36 am 
Yes, elevation changes have a major effect on air pressure. Who hasn't returned to sea level from a 5000-ft trailhead to find half-empty water bottles collapsed? And temperature also has a major effect, as can be easily demonstrated by holding your pad in your hands as you quickly move it toward a fire or heater. It will swell noticeably in a matter of a second or two. Barometric pressure changes are considerably smaller (hurricanes and tornadoes excepted). An approaching storm may change the barometric pressure by the equivalent of 200 to 500 feet of elevation overnight, which is barely--if at all--noticeable in your air mattress.

thunderhead, Cyclopath
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pula58
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PostMon Aug 08, 2022 4:00 pm 
neek wrote:
Note the reverse can happen too. I returned to the tent one hot afternoon last week to find my pad about ready to explode.
Yes, that can happen. Best to partially deflate the pad if it is going to get warmed up by being in the sun, or being in a tent that is in the sun.

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thunderhead
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PostTue Aug 09, 2022 2:07 pm 
texasbb wrote:
Yes, elevation changes have a major effect on air pressure. Who hasn't returned to sea level from a 5000-ft trailhead to find half-empty water bottles collapsed? And temperature also has a major effect, as can be easily demonstrated by holding your pad in your hands as you quickly move it toward a fire or heater. It will swell noticeably in a matter of a second or two. Barometric pressure changes are considerably smaller (hurricanes and tornadoes excepted). An approaching storm may change the barometric pressure by the equivalent of 200 to 500 feet of elevation overnight, which is barely--if at all--noticeable in your air mattress.
Well written. Temperature is indeed your primary culprit if your pad deflates a little as temperature drops, especially if you inflate with your mouth. Human body temp is 37C. As that drops to say 10C (a relatively warm night in most cascades camps), youll lose 10% of the pressure in the pad. I generally inflate my pad twice... topping off after the initial temp drop.

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