Natural thermal insulation materials developed from renewable crop by-products and natural binders are analysed in terms of their thermal degradation and fire behaviour. A Pyrolysis Combustion Flow Calorimetre (PCFC) is used to characterise some kinds of crop by-products, including rice husk, corn pith and barley straw. This technique is complemented with a TG analysis. Six thermal insulation materials, formulated with such crop by-products and two kind of natural binders, corn starch and sodium alginate, are developed and analysed. PCFC results show an improvement when sodium alginate is incorporated, especially in the corn pith composite. Fire reaction tests are also performed that yield results which are in qualitative agreement with the small-scale tests.