For the reinforcing of castable refractory the stainless fibres are the industry standard. The very fast increase of temperature and the huge difference in in thermal conductivity compared to refractory means that large diameter steel reinforcing is unsuitable, whereas the small diameter produces a much greater surface area to the surrounding refractory to disperse its heat into. Stainless is the preferred material because steel exposed to heat increases corrosive reaction.

For those folk trying to source these fibres, they may find that the minimum quantity suppliers will deal with coupled with the high price to be prohibitive. I buy them as a minimum quantity of 20 kgs and the price works out to $20/kg. They are 25 x 0.5 mm. Because 20kg is probably way too much (@2% by weight) and you may not be able to source smaller quantities, here is a possible alternative solution. It is Stainless steel rigging for yachts available at all ship chandleries, who will sell by whatever length you require.

It is surprisingly easy to cut with an angle grinder fitted with a steel cutoff disc to whatever lengths you require and then unravelled into 7 smaller strands , each of which can be further unravelled into 7 even smaller strands.
Conveniently they come out quite crimped because of the twists. I think this is an advantage because it provides greater pull out resistance.I used a length of 5mm stainless rigging wire which made up 49 curly strands each around 0.3 mm thick.
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