Scorch Marks

Scorch marks are something that any thermal insulation jacket, mattress or cover manufacture will be accustomed to, but what are they? And why do they occur? We created this document to simply explain the cause. 

Scorch marks are the darkened ‘char-like’ colouring that occurs when a fabric has been in contact with a hot surface which has started the thermal degradation of a compound. These are generally wrongfully identified as fire residue, which can also be linked to fuming or outgassing. 

These marks can be caused from a variety of things, the simplest form of scorch mark is that of the sizing (the lubrication used on yarns during weaving) which has a very low thermal resistance and will start its thermal degradation process quite soon after heat exposure. 

Another cause of scorch marks can be from additional coatings which are applied to fabrics after weaving, such as weavelock or weaveset, PU, acrylic – these all have a low temperature resistance <150°C. High temperature treatments, such as vermiculite or silica wash, which range between 750°C and 1000°C*, may take longer to show as severe scorch marks, but the low temperature sizing’s and any binders and softeners used within the dispersion, will begin to thermally degrade first and may show on the surface. 

These marks are by no means the fabric ‘failing’ or a cause for fire concern. 

Another type of scorch mark is one that is caused by direct contact with fire. This again is signalling the thermal degradation of low temperature compounds on the fabric and does not necessarily mean ‘fire’ or fabric failure. One would expect to see scorching when in contact with direct flame, therefore when checking the fabrics integrity, if it is still flexible, intact, and otherwise un-damaged, then the marks are simply signalling some form of thermal degradation. 

A method to reduce the scorch marks on loomstate fabrics would be heat treatment, or caramelisation. HT or ‘caramelised’ fabrics have undergone a post-weaving treatment to thermally degrade the sizing’s. This causes the fabric to turn tan/beige or golden in colour. This also has the added benefit of reduced fuming, or out-gassing when first exposed to heat.

*vermiculite can withstand 1000°C but the fabric will have embrittled locally.