I dug out an old Thermarest non SI foam/inflatable pad that has been rolled up for around 30 years! I last used it on a camping trip with my Dad when I was in middle school. So anyway, the thing inflates and holds air (don't make 'em like they used to lol!).
One thing I noticed is that it doesn't appear to have a way to prevent air from escaping in between breaths. I honestly don't remember if this is how they were back then or if I need to replace the valve? The valve is a screw top if that helps. Can anybody chime in?