sorry, thread seemed derailed so I didn't pop in. Thank God
@The Chairman put a tagging feature in for stuff like this. I usually start ignoring threads after the third page or so unless I get tagged
Ok, so air is what we are using to insulate. Without using active materials like phase change materials that can heat/cool under certain conditions, we are using passive insulation to create an air barrier between the water and our skin.
The ideal solution is something pillowy because that has lots of air and will insulate very well. Downside of this is there is basically no resiliency to this kind of solution. I.e. it doesn't "spring" back when put under pressure, and it has no ability to insulate when compressed.
Next solution is to take something really resilient and make it lofty. Felts are typically how this is done i.e. things like polartec.
so, what happens here is that when the pressure from your suit goes against the fabric, the dense felt compresses less and ends up holding more air than the light pillowy fabric and gives you an extra barrier against the cold. This can be made better by things like hollow fibers *DuPont's Thermax* which holds some more air.
You want more insulation around your chest/belly than your back, but your front is where all of the pressure *or really lack of pressure from the air in the suit*. Dense is good in this case because of resiliency.