I think what I actually want to know is, from the same manufacturer say, how would 4/3mm suits compare if one was lined with poly fleece and the other wasn't...?
Regardless of the some of the silly comments made, the same suit lined will be noticeably warmer and just feel more comfortable than the unlined.
if it is some fleecy stuff its only positive quality is getting dry surface or quick dry feeling. actually this liner does not have much thermal insulation qualities at all
Yes that magical "fleecy stuff" is the very common polyethylene terephthalate (PET) or some mix (although different manufacturers will use different marketing names: polar fleece, Polar Tec, poly fleece, or just fleece). Like wool fleece retains about 75-80% of its insulating properties when wet. This is why for hundreds of years fisherman have worn wool and lined clothing with it in wet environments. A lot of the application is now moving to fleece which is not quite as warm put pound for pound is. Also it is cheaper, lighter, and non-allergenic. The other nice thing about fleece is that it is hydrophobic which means it does not absorb water and moves that water away from your body.
So how much warmer:
With 0 being a perfect insulator still air has a thermal conductivity of 0.024 W/mK
Closed cell neoprene has a thermal conductivity of 0.054 W/mK
Polyester fleece is about 0.15 to 0.24 W/mK
So it is about half to a quarter as insulating as neoprene. But it is cheap, light, flexible, and comfortable.
You can test this for cheap. Get yourself a fleece lined rash guard, and ask yourself if it is keeping you much warmer than a non lined rashguard. If you do not have a lined suit, get a long sleeve one they are warm, comfy, and make it easy to put your suit on.
like thin layer of metal coating would reflect the heat of your body back to the body? hilarious!
all the metals are pretty much best heat conductors in the universe and when the metal is in touch with your skin you are pretty much conveying your body heat strait to the neoprene! just like there was not the "high tech" titanium layer at all! and i'm pretty much confident there is no titanium in the "titanium reflective layer" at all
Eree obviously did not make it through 8th grade physics, and not too observant of the world around him. This technology and principle is seen everywhere in our daily lives: home insulation, HVAC, water tanks, glass thermoses, computers, food storage and shipment, electronics, medical applications, automotive, space, etc. What Eree should have learned in middle school is that heat is transferred by convection, conduction, and radiation. Radiant insulating barriers are put over top of mass conductive insulators like neoprene. This is why the inside of a glass thermos is silver and why you will see basically bubble wrap with a foil coating used in home insulating and soft coolers. Really like you have never seen home insulation with silver foil or your air condition wrapped in foil. And as mentioned you will see this in space blankets, tents, and other outdoor apparel. I am not sure of the overall efficiency of this concept in wet suits since the movement of water and conduction will far outweigh the loss due to radiation. These are more used in deep diving dry suits. However in a well-sealed wetsuit this will add warmth. I am pretty sure these liners are in fact titanium oxide, and I am not sure why people are in such disbelief like it is gold foil or something. Probably talking a few cents worse of titanium. It is just not that expensive. You can also test this cheap. I have a lined rashguard with hood and it works well.
And again this is an apple to apples comparison. The most important thing in warmth is limiting the amount of water movement. So fit, stitching, design (neck locks, leg and arm locks, flushing panels, etc), are more important features.