Swiss (SMBC) and Italian (IMBC) are both meringue-based. Hence, they both have whipped egg whites before the addition of butter. And, the main difference between the two is in the process used to make the buttercreams. - In this SMBC, the egg whites are combined with sugar and heated over a double boiler until all the sugar has melted. - IMBC, on the other hand, uses a thick sugar syrup that is poured into the whipping egg whites. And, it is very important to use a thermometer to ensure you have the right temperature for the sugar syrup. - Some say IMBC holds up better in humidity due to the boiling sugar syrup.