Which natural fiber is fire resistant by nature?

The best fire resistant fiber by nature is seaweed fiber. Its LOI can reach 48%. And it burns without smoke and odor. Seaweed fiber is sustainable and 100% organic. Seaweed fabric is suitable for 4 seasons.

The second natural fire resistant fiber is wool. Its LOI is around 26%. It  burns with smell as it's a kind of protein based fiber. Wool fabric is usually for spring, autumn and winter. 

Silk is also a protein based fiber. The LOI is around 21%. It also burns with smell.