Intumesce
Intumesce , intransitive verb
[Latin intumescere; pref. in- in + tumescere to swell up, incho. from tumere to swell. See Tumid.]
To enlarge or expand with heat; to swell; specifically, to swell up or bubble up under the action of heat, as before the blowpipe.
In a higher heat, it intumesces, and melts into a yellowish black mass.