Flannel sheets are definitely your best bet for keeping warm. It's a heavy, tightly-woven fabric that is ideal for retaining your heat.
Heavycotton sweatshirts or even ones made of wool would be best for keeping a person warm.
a warm blanket in a cage
Flannel sheets provide warmth because the material retains the heat that it comes in contact with, which means a person's body temperature will warm the sheets and keep them warm.
Flannel sheets are excellent for keeping a sleeper warm throughout the night. In the winter, they can add an extra layer of warmth, compared to a duvet alone, and in the summer flannel sheets may serve instead of a duvet or blanket for a cooler sleep.
warm places
a warm blanket in a cage
Keeping warm is not a change - of any sort.
Koalas have no problems keeping warm. Their fur is specially insulated to keep them warm in cold weather, and cool in hot weather.
Foil itself will not warm it, it has to already be warm for it to insulate it.
Warm and sunny weather is best for growing roses.
For keeping it warm
depends on what kind of bottle. if its a regualr plastic bottle keeping it under your armpit will keep it at around 96 98 degrees.