The invention provides a method for making MMV fibres from a charge which comprises a mixture of at least two types of briquettes. The overall chemical analysis of the briquette mixture gives initial melting temperature (I) when provided in the form of a single type of briquette. This single type of briquette also gives compression strength (i) over the operating temperature range 1,200 DEG C to 1,340 DEG C. The briquette mixture charged to the furnace is such that at least 30 wt.% of the charge is in the form of briquette which have IMT at least 20 DEG C greater than IMT (I) and/or is such that at least 30 wt.% of the charge comprises briquettes having compression strength over the working temperature range greater than compression strength (i) at each temperature.