I have owned numerous cags, semi-dry cags, dry cags and dry suits over the years. Neoprene seals, latex seals – all have been tried and tested for years and in reality none have ever been 100% dry.
At the end of the day I believe that it’s all relative, if the cag fits right and the seals are constructed or even trimmed to give a good water tight seal you will only ever minimise the chance of water finding its way inside. In some cases the amount of water entering the cag is so small it is virtually dry, but will never be totally dry.
Personally I find that I always get a little water entering the neck seal. Not piles of of water just the odd drip and this has always been the case. I think this is down to the way the seal sits on my neck as I paddle and move.
I have reached the point where the cags I have are pretty much bomber and are as good as dry, even my Immersion Research LX (Semi-dry) with only a neoprene neck is almost as dry as the other cags that I have in my gear bag. The cag that I use the most and is probably the best bit of kit I have is the new Sweet Shadrach cag. Other than the odd drip from the neck the cag is as good as water tight. The image above was taken after a bit of swimming practice in the Tees. Despite swimming and jumping into the water I remained pretty much dry from the waist up.
You also need to consider that even the most breathable piece of gear will not be able to cope fully with high physical activity in a humid environment. I.E. fully cope with the amount of sweat produced by the wearer. If you are wet inside of your dry gear then it may not be due to a failure of the waterproofing properties of the product.