A heat insulator that generates no smoke when incinerated, has a low calorific value, and achieves a desired dimension and heat insulation performance is provided. A heat insulator 1 is formed by heat-mixing, in an extruder 11, a paper pellet 7 that is a mixture of a fine paper powder having a particle diameter of 30 to 200 μm and starch, a container recycle pellet 8 that is a mixture of polypropylene, polyethylene, and polystyrene, foamable polypropylene 9, and water 10 to obtain a plate-like foamed product 2, and orthogonally overlaying a plurality of plate-like foamed products 2. A weight distribution is set so that the paper pellet 7 is 50 to 65% by weight, the container recycle pellet 8 is 13 to 25% by weight, the foamable polypropylene 9 is 10 to 30% by weight, and the water 10 is 10 to 20% by weight to these resins and other materials.