Ski Goggle Fogging Question

Here is a chat transcript about single versus double lenses and fogging with ski goggles and prescritpion.

shannen: Hi, How can I help you today?
Visitor: I'm looking for a ski goggle that has a single prescription lens
shannen: The way the ski goggles work is there is a piece that carries the prescription and snaps inside the goggle. There is no technology for a full shield type goggle lens to have a prescription made into it. The only other option is for a sunglass type with foam where it has two separate lenses for the prescription to be built directly into the lens.
Visitor: The problem with two lenses is that the inner one tends to fog when one stops skiing.
shannen: You'll have more tendency to fog with a single lens than a double.
shannen: The point of a double lens it to prevent fogging.
shannen: The more temperature difference between the inside of the lens and the outside of the lens causes the fogging.
Visitor: Ok.  What are my options for a prescription solution?
shannen: So with a single lens, you have a larger difference between outside and inside temperature. The double lens provides a layer between your hot face and the cold air preventing fogging.
shannen: The best thing for fogging is the Smith Turbo goggle with the prescription insert.
shannen: The Turbo is a microfan inside the goggle that constantly generates wind to keep the lenses defogged.
shannen: The more airflow, the less chance of fogging. That is why you fog when you stop. You don't have the airflow anymore.
shannen: The fan keeps airflow going even when you stop.
Visitor: does it require a battery?
shannen: It does. It takes one AAA battery.
shannen: battery pack is integrated into the strap.
Visitor: Are there different types of turbo fan goggles?
shannen: Different styles? yes.
Visitor: Which style so you recommend?
shannen: Style wise is just personal preference. They fit different sized head as well. And then the Knowledge one is designed to fit over glasses.
Visitor: It looks like smith has several options for the lens types.  Which is best?
shannen: Depends on lighting conditions. The Ignitor is there best all around lens for various lighting conditions. The Sensor Mirror is more for low light and the Platinum mirror is more for bright light.
Visitor: From the pictures I've seen there are two options for the lenses, an insert and a attached (direct).  Either will work with the ignitor.
shannen: no there is no direct in option for the prescription lenses. There is the insert by itself with no lenses, then the insert with us making the prescription lenses. Those are the only two prescription options.
Visitor: So there is only one type of insert lens not two types that I was led to believe
shannen: no one type of insert.
shannen: I see on their site they offer the Uvex goggle. We used to offer that but it has been discontinued by the manufacturer so nothing like that left. If they have some it is old stock. It was discontinued about 3 years ago.
Visitor: Ok so how much is the Smith Phenom Turbo Fan model with the ignitor lense and does it come with the fog free coating?
shannen: You have to add the fog free coating for $65 more.
shannen: Goggle is $170.
Visitor: So the total cost is?
shannen: So $170 for goggle, $115 for insert with Rx lesnes and if you add the anti-fog coating, it would be $65 more for a total of $350
Visitor: Can I purchase these on-line?
shannen: yes.
shannen: http://www.sporteyes.biz/cart.php?m=product_detail&p=713
Visitor: Thank you Shannen, I'll get my prescription from my doctor tomorrow.
shannen: you're welcome.