Traditionally, tea bags have been square or rectangular in shape. More recently circular and pyramidal bags have come on the market, and are often claimed by the manufacturers to improve the quality of the brew. This claim, however, only holds with a proper preparation.
A practical observation in the development of the tea bag from the traditional square, to the circular and finally the pyramidal bags is that the amount of adhesive used to seal the bags is reduced in each development. It could therefore be surmised that the development is not to improve the quality of the brew, but to reduce the cost of producing the bags themselves.
Well, these few ones aren’t definitely traditional.