There are only 3 ways to provide "insulating value" to any product on the market when needed.
1.Pull it into a vacuum (suck the air out).
2. Dead air space. Stop the air from moving around inside a sealed chamber or cavity.
3. 100% foam fill the chamber.
A dead air space can only be achieved inside small cavities or chambers (like in vinyl windows and vinyl sliding patio door frames in a honeycomb type fashion.
But when a cavity is too big it's no longer a dead air space, so to keep the air from moving around inside you have to 100% foam fill it.
Products for homes that need this to provide insulating value are entry doors made out of fiberglass or steel, refrigerator and freezers, seat boards on bay and bow windows as well as garden windows, garage doors, and between the studs in your walls just to name a few.
Vinyl window frames don't need it because the cavities inside are small enough to create "dead" air space which in itself provides sufficient insulating value.
Companies putting a bit of foam in the frame only do it for "consumer appeal" and to try to add more strength to the frame because they chose not to use more chambers.
Compare U-factors when having companies come out because whoever has the lowest U-factor has the more efficient window; whether there's foam in the frame or not.
