SOUFA was brushed on to tissue paper, and after drying it was ignited with an alcohol lamp.
SOUFA was brushed on tissue paper and ignited with an alcohol lamp after it had dried.

SOUFA gives high flame resistance to cellulose, so it is easy to stop burning. However, SOUFA does burn. The cellulose will burn, but it won’t burn any more. Since the cellulose becomes crispy, SOUFA with a lower concentration seems to be sufficient.

As for the mechanism of flame retardancy, SOUFA settles on the cellulose of the pulp and reacts to heat when heat is applied, and forms a thin glass film on the cotton surface. At the same time, it combines with the carbon of cotton to form an oxygen-blocking film. Even if it is roasted with a burner, it does not form a hole.
Therefore, once it is burnt, it will not spread further. It does not have much effect on the texture if it is only brushed on.
However, if too much is applied, it may become hard. This is because the boric acid has a property of slightly hardening cellulose.