Final answer:
The substance in question is likely an organic polymer material, characterized by its toughness and lightness, with low melting points making them sensitive to heat and potential damage by solvents.
Step-by-step explanation:
The description provided suggests a substance that is tough and light, and has a tendency to melt when heated or exposed to flame. It also indicates that this material can be damaged by solvents. Considering the additional information given, it appears the substance shares characteristics common to certain organic polymer materials such as certain plastics or resins. These materials often possess qualities such as being tough, lightweight, and having low melting points, making them susceptible to damage from heat and certain chemical solvents. Furthermore, the mention of being 'used for high-temperature applications' such as in furnace tubes implies it could be a type of synthetic polymer designed for higher resilience to heat but still having the mentioned vulnerability to solvents.