a disposable or reusable and reclosable thermoplastic bag capable of being compactly stored as a food container in freezers , yet capable of standing with an upright spout in a microwave oven for non - spill thawing and cooking of food contained in the bag . the bag is formed of two wing - shaped pouches on either side of the upright spout . the preferred closure is a zipper type which can automatically vent upon softening of its thermoplastic structure during the cooking stage . the bag preferably has inner and outer skin layers of different heat - softening temperature responses so that peripheral sealing is effected only with the inner layers , allowing the wing - shaped pouches to be formed out of a gussetted bottom without sealing of the outer layer plies facing one another .