Niuniu is a big warm bag, a bit heavy, but very comfy.

牛牛是个大暖包，有点儿沉，却很舒服喔。

youdao

This sleeping bag is very warm.

这条睡袋很暖和。

《牛津词典》

Giving herself no time to think, Anna carefully picked up her mother's worn bag and hung it around her neck. Then she flew out of the house and down, down to the warm human world below.

没有时间容她多想，安娜小心翼翼的拿起妈妈那个旧包挂在自己脖子上，然后，她飞出房子，直往下飞，来到了充满温暖的人间。

youdao

Inside, keep your body off the ice or ground (the Inuit put their sleeping blankets on top of a bed of sticks and reeds) and create heat-trapping "loft" (it's what keeps you warm in a sleeping bag) by layering a few small blankets or big trash bags, with leaves or crumpled newspapers in between.

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Firefighters turned on a portable heater to keep her warm in near-freezing temperatures while they dropped an air bag into the opening to slightly spread the walls.

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