Delaying the melting of an ice cream

How to delay the melting of an ice cream, a sherbet, a sorbet ?

Melting depends on the thermal conductivity and of the heat capacity. But without changing the composition of the ice cream, one cannot change one or the other.

On the other hand, a foamy structure around the ice cream can be very protective. For example, if you heat some whipped egg white with a burner at 1000°C, a thermometer inside the foam shows that the temperature increases very slowly.