Fully lined, front and back. Feels solid! Need to swim in it for a while to see how durable it is, but it feels pretty durable.Comfortable and pretty modest. The sides are about 3-4 inches. I like slightly narrower sides for comfortable leg movement, but they don''t pinch my thighs. I''m a 34 waist and usually get suits in  a 32. The 32 for this suit is just right. Snug without being too tight.