I noticed being much warmer at depth than when shallow at the end of a dive in a drysuit. Has anyone noticed this or is this due to some specific factors I experienced as in it was all in my head? When at depth with a drysuit, do you have a better air barrier insulating your body than when at shallow water? Maybe this is related to not being able to have as much air in the suit at the end of a dive since I dive with Al 80s?
Perspiration is a factor- when suiting up you get all sweaty, by the end of the dive the sweat is still in your suit- your better off if you have wicking undergarments next to your skin like under armer. When you get to the surface your warm air barrier is less- but once your topside you can add some air and will feel much better. Just the nature of diving dry- layer up if your too cold by the end of a dive.
If I get a chill its on the return. I've attributed it to venting all the warm air out. Then adding a bit of cold air if I swim around the shallows. At the tail end of dives I may swim an extra 30 minutes between 15 and 30 so I need to vent/add little bits and that cools me down.
You didn't mention what "depth" you are talking about but this could be related to nitrogen narcosis. When you descend deeper on air it's like taking a couple shots of liquor. You get a nice warm buzz. When you ascend the narcosis wears off and you feel the full effects of the cold environment again.
On the way up, the gas in the suit expands because the ambient pressure is being reduced as you get shallower. That will cause the temperature of the gas in the suit to go down (this is a law of thermodynamics). I'm sure that accounts for part of this effect. I've noticed it too.