Utensils To Use When 'Folding'
When a recipe asks you to ‘fold’ (such as when incorporating whisked egg whites into a base mixture) the best utensil to use is either a large metal spoon or silicone spatula. Their clean ‘slicing’ edge are the most suitable to use to cut through and gently combine mixtures so that as little of the incorporated air is lost and the mixture doesn't become ‘heavy’ due to over-mixing.
One of my favourite types of spatulas to use when folding is a ‘spoonula’ (basically a spatula with a shallow bowl like a spoon) which makes light work of folding mixtures, transferring them to cake pans and then scraping the bowl. It is well worth getting hold of one (or three!) of these if you don’t already have a spoonula!