So I am a little confused. First, is the inside of the bottle the aluminum or is it the polyethelene? Second, does anyone know if when you put cold water or any beverage for that fact in it, does it sweat? Thank you in advance for your help

Never noticed the bottle with sweat and I use it for cold beverages all the time.

http://www.ecovessel.com/_catalog_63883/Insulated_Vacuum_Sealed_25_Ounce_Bottles This is a vacuum sealed insualted, sweat-proof water bottle that I found online. You can check it out. This is from the eco vessel site: Our Eco Vessel insulated stainless steel water bottle is vacuum sealed with 2 layers of #304 grade stainless steel and is made to be used as a thermos for both hot and cold beverages, maintaining the desired temperature for several hours. Feel secure knowing that our 100% recyclable bottles are BPA-free, and are designed for your safety, ease of use, and convenience.

The inside is not polyethelene, it is lined with a BPA Free Poly Aramide lining that has been third party tested, according to the Laken USA website. I like it because it does not hold taste. It might sweat a little because the foam that lines between the two layers of aluminum is not as thermally efficient as a vacuum, but I have never seen a vacuum double wall aluminum bottle.