Glass is a very good conductor of heat, though as many have said, it takes a lot more time, to heat it to the same temps. The advantage glass has, is it retains heat better than SS, makes a better heat insulator (depending on usage) and correct me, if I'm wrong guys... I believe glass distributes heat better/evenly, over its entire surface, than SS when using a single heat source that concentrates heat to an area/part of a glass or SS cylinder. Though, with say a wrapped coil heating element around the glass and SS cylinders... I don't know what/if glass would have an advantage at that point.
Glass is not a particularly good conductor of heat. Stainless steel conducts heat a bit better. Aluminium conducts heat a lot better. When I designed the pod, I chose to use glass to contain the resistor because I want as little heat as possible seeping away from the hot spot. What I have discovered from the work of others and my own experiments is that the air reaches maximum temperature once it passes over the resistor. This is the hottest part of the whole system. Every other part of the vape is at a lower temperature than this. In fact, every other part of the vaporizer is pulling heat away from the heat source, reducing its efficiency. For this reason I have decided that heatsinks, fins, etc are of no advantage and may instead cause energy to be wasted. There is some preheating of the air as it first passes through these parts but I believe that this offers no advantage to its final temperature. If it were possible I would prefer to contain the resistor with a material that had zero thermal conductivity. That way I could be sure that all of the heat energy from the resistor is being dissipated into the airstream. Glass was the best material I could find for this purpose.
By having that one piece of silicone there you are effectively blocking off everything below it from the air path. On the other log vapes that hot air is hitting the inside of the wood (toxic fumes I'm told) and the solder and power plug area. Unless I am mistaken I think I'd rather hot air hit high temp silicone than charring wood and hitting the power plug area.
I think the fact that wood is natural might be hiding the fact that it is actually NOT something you want to be charring or even heating and inhaling. Lets keep in mind Datura is natural too and a horrible poison.
Looking at Dave's design I have no doubt that his intention is to provide the cleanest, safest air path possible. It is obvious that a lot of consideration went into this. While some people may not like the use of silicone, knowing the kinds of applications it is used in such as ovenware, aquariums, and medical implants, I consider it a particularly inert substance under a wide range of environmental conditions. Furthermore, Dave has even taken steps to isolate the silicone from the air path as well.
As far as the "other log vapes that hot air is hitting the inside of the wood", I only know of the PD, and my own vape that allow this. However, in the Hot Pod, air that has been in contact with the hot part of the wood does not make it into the air path because the air intake is at the cooler lower part of the pod. I don't agree with the idea that hot wood creates toxic fumes. Although you used datura as an example, I don't think anyone would design a vape made out of datura, or anything else known to be toxic. Indeed there are many toxic plants but they are also well documented and therefore avoided. My PD is made from cherry wood. If that is toxic then there must be a lot of toxic furniture, toys, etc out there. The PDs are known for internal charring, but how much of a problem is this in reality? Perhaps a tiny amount of wood smoke has entered the air stream at some point. While this is not a desirable feature, it is not toxic and hardly worth considering. Who hasn't sat around a campfire? For thousands of years mankind has lived with smoke and fire. I'm sure that most of us have breathed in a fair amount of smoke over our lifetimes, so it's worth maintaining some perspective and common sense.
The Banksia pods used in the Hot Pod are not toxic. The pods start off as nectar-filled flowers. The nectar of these flowers is a traditional food of the aborigines, as well as for a variety of animals and insects. The pods themselves have been used by woodturners for decades. If there were any toxicity in the pods then those guys would be ingesting it big time and it would have made news long ago. As you can see from the photo in my previous post, the Hot Pod has a large internal space. This was a deliberate design decision to ensure that charring does not occur. The sides of the pod are just too far away from the heat source for this to happen.
EDIT: Forgot to mention solder. I believe that all the vape makers use lead-free solder. This solder is composed of copper and tin. Neither of these elements are toxic. Copper is often used for water pipes. Tin is used extensively as a coating for cans containing food. Again, these uses have long histories.