Googled and found this.....hope it helps you! Here is the link, incase you want to read more about it. http://www.baking911.com/decorating/cakes_buttercream.htm#meringue
Swiss Meringue Buttercream is made by heating the egg whites, sugar and cream of tartar in a waterbath until the sugar is dissolved and then transferred into the mixer and whipped until a stiff foam foam until they reach a temperature of 160 degrees F, for 2 to 4 minutes, where the egg whites are considered "cooked". It is then beaten with butter to make a buttercream meringue. The result is always a beautiful, white buttercream that you can get really smooth on a cake. In warm weather, it doesn't hold up as well as Italian Meringue Buttercream does, but you can make it with hi-ratio shortening so it will be more stable in temperatures over 80 degrees F. See
Italian Meringue Buttercream is more popular than Swiss Meringue Buttercream. After the meringue is whipped to stiff peaks, and in the case of the Italian Meringue, cooled to room temperature. is made with softball (240 degree F) sugar syrup poured into whipping egg whites. Once whipped, add softened butter to the bowl, little at a time and whip until a fluffy consistency is reached. You can make the icing in advance; keep it in an airtight container in the refrigerator for a week. Italian Meringue Buttercream can be frozen for up to 3 months.
As to whether Swiss or Italian Meringue Buttercream is "better", that is up to its use. Because Swiss meringue isn't made with a sugar syrup as Italian Meringue Buttercream is, you don't have to worry about little crystallized bits of sugar that you can get with an Italian Meringue. The primary difference between Italian and Swiss Meringue Buttercreams is stability or how well they hold up in all situations. Swiss tends to deflate slightly faster and doesn't hold up as well in warm environments. Italian is more dependable and heartier. Either can be frozen for long-term storage. Both types of Buttercream often take quite a bit of whipping in order to reach the right consistency of light and fluffy. Cool butter is whipped in and many times the meringue buttercream breaks, but with more beating it comes together and makes a silky, very buttery, not too sweet or grainy buttercream.