No winter boot will keep your feet warm, no matter the price, if it is fit too small!
A traditional Duck Boot will have a waterproof rubber foot. This type of boot is designed to keep your foot dry while trudging through wet lands during duck hunting. Since this boot keeps your foot dry it was easy to add insulation and make it adaptable to colder weather.
A Pack Boot always has an insulated removable lining. This removable felt pack can be taken out to let dry or wash. You should fit the lining larger than your foot. The lining is also smaller than the outside shell. This system allows for ultimate warmth. The inside of the shell is warmer than outside and inside the lining is warmer than inside the shell.
Winter boots get their warming properties from various insulation types. First there are synthetic insulations like Thinsulate , PrimaLoft and Omniheat which are all some type of man made spun fiber. Second is natural types of insulation which includes fur, wool pile, and wool felt. Last there are man made reflective insulations which redirect heat from your foot back to your body. Your winter boots will have some type of these insulations or combination of insulation types.
Keeping your feet dry is key to having warm feet. Boots can be made waterproof by using a fabric like gortex. A full boot sock will be made of this waterproof fabric then worked into the design of the boot. Another way to waterproof footwear is to use waterproof leathers. True waterproof leathers are treated during the tanning process. However there are various sprays, oils, and waxes that will waterproof leather post tanning. Finally the seams of the boot have to be sealed so water wont seep in. Seams are sealed using waterpoof taping. If you find you still continue to have wet feet it is probably due to moisture coming from your own body. Feet can sweat up to a half pint per day. A good sock is your best defense. Stay away from cotton as it holds moisture next to the skin. Go for wool or acrylic which will wick moisture away from the foot.