Thermally expandable compositions comprising a chemical blowing agent

A thermally expandable composition comprising:

• a) a thermoplastic polymer component P and/or an elastomer component E,
• b) at least one chemical blowing agent BA comprising at least one dicarboxylic acid salt of an aminoguanidine compound, wherein the at least one chemical blowing agent BA is present as solid particles having a d90 particle size of not more than 350 μm and has a maximum decomposition peak temperature measured by Differential Scanning calorimetry (DSC) in a range of 135° C.-250° C.,
• c) optionally at least one free radical initiator I and/or a vulcanization system VS, and
• d) at least one guanidine derivative G different from the at least one dicarboxylic acid salt of an aminoguanidine compound, the at least one guanidine derivative G being present in an amount in a range of 1 to 5 wt.-% based on a total weight of the thermally expandable composition,
• wherein the aminoguanidine compound is represented by formula (I)
• wherein R1 and R2 represent independently from each other a hydrogen atom or an amino group.