To provide a impervious heat-reserving board at a low cost, having excellent water-impervious heat-resisting properties and capable of being easily recycled as waste paper.
This impervious heat-reserving board has a lamination comprising at least three layers of fibrous material and is characterized by that the second layer from the wrapped package-contacting side contains thermally expandable particles and has 0.2-0.5 g/cm3 density. And, preferably, the thermally expandable particles are expandable microcapsules having 5-30 μm average diameter and expandable to have 4-5 times diameter and 50-130 times volume by heating at 80-200°C and contained at a rate of 1-30 wt.% based on the oven dry basis equivalent weight of the inner layer wet paper.
MIZOBUCHI HIROSHI
IWAMA FUMIHIRO
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