Abstract: Disclosed is a thermally expandable composition, comprising at least one polymer P, cross-linkable by peroxide, and between 1 wt.-% and 2.5 wt.-%, based on the total weight of the composition, of at least one acrylate A, and between 0.2 wt.-% and 2.5 wt.-%, based on the total weight of the composition, of at least one peroxide, and at least one blowing agent, characterised in that the equivalent ratio of said peroxide to said acrylate A is between 0.01 and 0.5, preferably between 0.13 and 0.41, and the weight ratio of said peroxide to said acrylate A is lower than 0.33 and said polymer P comprises or essentially consists of at least two polymers PI and P2, wherein PI exhibits a melt flow index (MFI) of between 100 and 200 g/10 min, and P2 exhibits a melt flow index of between 0.1 and 60 g/10 min, wherein MFI is determined by ASTM D1238.

Abstract: A thermally expandable composition, including at least one polymer P, cross-linkable by peroxide, at least one peroxide, preferably at least one acrylate, at least one blowing agent B, preferably at least one activator for the blowing agent, and at least one epoxide group terminated polymer of the formula (I), wherein Y represents a n-valent radical of a linear or branched polyurethane polymer terminated with isocyanate groups after the removal of the n terminal isocyanate groups, Z represents a (1+m)-valent radical of an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide containing a primary or secondary hydroxyl group after the removal of the hydroxyl group and m epoxide groups, m represents an integer with a value of 1, 2, or 3, and n represents an integer with a value from 2 to 4.

Abstract: Disclosed is a thermally expandable composition, comprising at least one polymer P, cross-linkable by peroxide, and between 1 wt.-% and 2.5 wt.-%, based on the total weight of the composition, of at least one acrylate A, and between 0.2 wt.-% and 2.5 wt.-%, based on the total weight of the composition, of at least one peroxide, and at least one blowing agent, characterised in that the equivalent ratio of said peroxide to said acrylate A is between 0.01 and 0.5, preferably between 0.13 and 0.41, and the weight ratio of said peroxide to said acrylate A is lower than 0.33 and said polymer P comprises or essentially consists of at least two polymers PI and P2, wherein PI exhibits a melt flow index (MFI) of between 100 and 200 g/10 min, and P2 exhibits a melt flow index of between 0.1 and 60 g/10 min, wherein MFI is determined by ASTM D1238.