Replacement Window Companies are quick to insult Aluminum Frames.
For good reason, but let's talk about the exception to the Rule.
Thermally Broken Aluminum Frames take advantage of Aluminum's strength and durability while minimizing what we don't want---transmitting of heat.
Aluminum is 40x as strong as wood, and 4x as strong as Vinyl.
Aluminum Frames can therefore be thinner and less bulky than Vinyl and even allow for replacing a choice few windows without looking strikingly different than the old Builder Grade Windows.