The Straight Dope

Go Back   Straight Dope Message Board > Main > General Questions

Reply
 
Thread Tools Display Modes
  #1  
Old 08-15-2004, 05:30 PM
dnooman dnooman is offline
Member
 
Join Date: May 2003
Location: Columbus, Ohio
Posts: 4,750
How do self-inflating camp mats work?

Apparently you just open a valve and it inflates, how?
Reply With Quote
Advertisements  
  #2  
Old 08-15-2004, 05:43 PM
Crafter_Man Crafter_Man is offline
Guest
 
Join Date: Apr 1999
I could be wrong about this, but I don’t think they “inflate” in the same way a balloon is inflated.

When you roll up the mat, you’re squeezing out the air. When you unroll the mat and open the valve, the structural rigidity of the mat opens a space (or gap) between the mat’s top side and bottom side. When this happens, it creates a weak vacuum, and air rushes in (through the valve) to fill the space. The air stops entering when the pressure in the gap equals the outside pressure. You then close the valve. The structural rigidity of the mat, in combination with closed air space in the gap, makes for a nice cushion.
Reply With Quote
  #3  
Old 08-15-2004, 05:57 PM
Johnny L.A. Johnny L.A. is online now
Charter Member
 
Join Date: Jan 2000
Location: NoWA
Posts: 48,791
To expand on what Crafter_Man said...

The inside of the mat is filled with "foam rubber". (Speaking generically, not technically.) When you roll the mat up, you not only force out the air but you also compress the foam. When you close the valve, the foam cannot expand because it's in a relative vacuum. When you open the valve the foam expands, drawing air in through the valve.
Reply With Quote
  #4  
Old 08-15-2004, 06:07 PM
Crafter_Man Crafter_Man is offline
Guest
 
Join Date: Apr 1999
Quote:
Originally Posted by Johnny L.A.
To expand on what Crafter_Man said...

The inside of the mat is filled with "foam rubber". (Speaking generically, not technically.) When you roll the mat up, you not only force out the air but you also compress the foam. When you close the valve, the foam cannot expand because it's in a relative vacuum. When you open the valve the foam expands, drawing air in through the valve.
Oh, so there's foam inside! That makes more sense, as it would be a bit tricky to design a mat with enough structural rigidity to create a 100% air gap.
Reply With Quote
  #5  
Old 08-15-2004, 06:09 PM
Squink Squink is offline
Guest
 
Join Date: Oct 2000
To expand on what Johnny L.A. said...
The mats employ open cell foam, which means that the airpockets that make up the foam are open at the surface, and connected to all the airpockets inside the foam. Closed cell foams are much more difficult to compress, as you must compress the air within them, rather than simply expell it.
Reply With Quote
  #6  
Old 08-15-2004, 06:56 PM
Magiver Magiver is offline
Guest
 
Join Date: Apr 2003
You would only use one if you were HIKING to a campsite. They are 1 step above sleeping on the bare ground. Get an inflateable if you don't have to carry it far (said the middle-aged man).
Reply With Quote
  #7  
Old 08-15-2004, 07:45 PM
dnooman dnooman is offline
Member
 
Join Date: May 2003
Location: Columbus, Ohio
Posts: 4,750
Quote:
Originally Posted by Magiver
You would only use one if you were HIKING to a campsite. They are 1 step above sleeping on the bare ground. Get an inflateable if you don't have to carry it far (said the middle-aged man).
Sage advice. Thanks. Also thanks for the other answers, I never thought it might be foam in there. I figured it was some sort of vacuum thing, just not quite sure.
Reply With Quote
  #8  
Old 08-15-2004, 07:53 PM
Richard Pearse Richard Pearse is offline
Member
 
Join Date: Aug 2001
Location: Kiwi in Adelaide
Posts: 8,090
Speaking from experience they are actually a couple of steps above sleeping on the ground. Those thin strips of dense foam that roll up small enough to sit on top of your pack are one step from sleeping on the ground. Unfortunately inflateable mattresses (airbeds) get very cold when it's cold, and very hot when it's hot, ie they have very poor insulation.
Reply With Quote
  #9  
Old 08-15-2004, 08:53 PM
Magiver Magiver is offline
Guest
 
Join Date: Apr 2003
Quote:
Originally Posted by 1920s Style "Death Ray"
Speaking from experience they are actually a couple of steps above sleeping on the ground. Those thin strips of dense foam that roll up small enough to sit on top of your pack are one step from sleeping on the ground. Unfortunately inflateable mattresses (airbeds) get very cold when it's cold, and very hot when it's hot, ie they have very poor insulation.
From personally experience (2 weeks ago) I agree. You have to bring the CORRECT temperature sleeping bag. A 55 deg night on an air mattress is a chilling experience unless you have a 35 deg sleeping bag or better. I would use a cot but I haven't found any that really like.
Reply With Quote
  #10  
Old 08-15-2004, 09:08 PM
Richard Pearse Richard Pearse is offline
Member
 
Join Date: Aug 2001
Location: Kiwi in Adelaide
Posts: 8,090
We used an airbed for a few days in the (tropical) north of Australia. As you say, being cold is easily fixed by using a sleeping bag. Being hot, however, is not fixable and is certainly not conducive to sleeping. Arggh, they were the worst nights sleep I've ever had, lying there, drenched in sweat, try move around and find a cool bit on the bed.
Reply With Quote
  #11  
Old 08-15-2004, 09:26 PM
Telemark Telemark is online now
Charter Member
 
Join Date: Apr 2000
Location: Hub of the sports world
Posts: 15,056
As someone who has been camping for many years, the Therm-a-Rest style open cell foam pads are a godsend. They are much more comfortable than the older closed cell Ensolite style pads. Granted, they are slightly heavier but the increased comfort is well worth the weight.

They come in a variety of thicknesses, from Ultralight to ones intended only for car camping. I own two, one fullsized for car camping comfort and a 3/4 length for backpacking. In winter, I carry a closed cell and an open cell for insulation from the snow.
Reply With Quote
  #12  
Old 08-15-2004, 09:37 PM
silenus silenus is offline
Hoc nomen meum verum non est.
Charter Member
 
Join Date: May 2003
Location: SoCal
Posts: 40,880
I have noticed that as the passage of years increases, my camping pad has as well. In my teens, a beat-up Ensolite pad was all I needed. In my 20s, I used a ThermaRest pad. In my 30s, I switched to an air-mattress, with the ThermaRest on top. Now, in my 40s, I don't bother with any of that. We car-camp most of the time, so I bought us an inflatable queen-size bed!

http://www.cabelas.com/cabelas/en/te...075&hasJS=true


And I don't feel guilty at all!
Reply With Quote
Reply



Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 09:28 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@chicagoreader.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Publishers - interested in subscribing to the Straight Dope?
Write to: sdsubscriptions@chicagoreader.com.

Copyright © 2013 Sun-Times Media, LLC.