# The Forensic Science of the Filament
The burn test is the fastest and most precise analytical method to differentiate natural polymers from synthetic ones without resorting to an electron microscope. By subjecting a fiber to heat, its molecular behavior reveals its origin: from plant cellulose to animal proteins or petroleum derivatives.
Cellulosic Fibers
Cotton and Linen burn quickly without melting. They smell like burnt paper because they come from wood or plants, leaving a volatile gray ash that scatters when blown.
Protein Fibers
Wool and Silk pull away from the flame. Their characteristic smell of burnt hair indicates the presence of sulfur and keratin. The residue is a black bead that crushes when touched.
Synthetic Fibers
Polyester and Nylon are essentially plastics. They melt forming a hot drop that hardens into a glassy bead impossible to break, with a sharp chemical smell.
# Chemical Evidence Matrix
A precise analysis requires crossing at least three pieces of evidence. Smell is the most reliable indicator for identifying blends: if a "linen" fabric gives off a slight plastic aroma and leaves hard residues, it indicates an undeclared polyester blend.
Laboratory Safety Protocol
Critical ventilation: Synthetic fibers release toxic gases when burning. Never perform this test in enclosed spaces.Immediate extinguishing: Always keep a container of water nearby. Some synthetic fibers can melt and adhere to skin.