PURPOSE: To obtain a foam for use as a damping material which comprises block copolyester by expanding a block copolyester comprising two specific polyester portions having specific physical properties.

CONSTITUTION: A block copolyester comprising a polyester portion A which is non-crystalline or has a melting point of 100°C or less, and contains as the main ingredients 60mol% or more aromatic dicarboxylic acid residue and a 5C or higher glycol, and a polyester portion B which is thermoplastic and has a melting point of 150°C or more, is expanded. The block copolyester has an impact resilience of 30% or less at room temperature. The loss tangent (tan δ) thereof has a maximum value of 0.05 or more in the temperature range of -20 to 40°C. Preferably, the resultant foam has a foam size of 1mm or less and an expansion ratio of 1.5 or more. Further, it is preferred that, when used as a damping material under conditions in which a damping time is 2 milliseconds or shorter, the foam would allow the dropped object to rebound only 3 times or less. It is also preferred that the foam have flexural modulus of 10MPa or more.