Heat insulating sheet

A heat insulating sheet comprising:

• a heat insulating body having a first surface and a second surface opposite to the first surface;
• and
• a first protective sheet disposed on the first surface of the heat insulating body;
• and
• a second protective sheet disposed on the second surface of the heat insulating body, wherein:
• the heat insulating body comprises a nonwoven fabric and xerogel,
• the nonwoven fabric is made of flame retardant fibers,
• the heat insulating body includes:
• a first region impregnated with the xerogel and carrying no thermoplastic resin;
• and
• a second region impregnated with a thermoplastic resin and carrying no xerogel, the second region is provided inside an outer periphery of the heat insulating body,
• the heat insulating sheet comprises a peripheral region provided outside the outer periphery of the heat insulating body, the peripheral region not containing the thermoplastic resin with which the second region has been impregnated and carrying no xerogel,
• in the second region, each of the first and second protective sheets are joined, and in the first region, the first and second protective sheets are not joined to the first region,
• a recessed portion is provided in the second region,
• in the peripheral region, the first and second protective sheets are joined each other,
• in an area of the first protective sheet corresponding to the first and second regions, a surface of the first protective sheet is entirely flat, and
• in an area of the second protective sheet corresponding to the first and peripheral regions, a surface of the second protective sheet is entirely flat.