The front of briefs and thongs are the same triangle, but the back of briefs is a bigger triangle, while the back of thongs is T-shaped. The back of the briefs covers the whole buttocks, while the thong is pulled in from the middle of the buttocks and tightly sticks to the anus. Personally, if the material is good and the T-shaped part is soft and elastic, thong is the most comfortable underwear.