Yes. They become hard as rocks when full. If they’re too full they may leak or if they’re full for too long you may develop plugged milk ducts and/or infection (mastitis) where one or both may become red, hot and very painful to the touch. When they are empty they may look and feel like deflated balloons. Sometimes when you hear another baby or think of your baby you may “let down”, which can feel oddly like when you feel a carbonated beverage going down your throat but instead it’s in your breasts. It is initially very painful since they crack and maybe sore, and even bleed. I remember having to stifle my screams into a pillow when I developed a laceration on one. It hurt like a mofo, and I have a high pain tolerance. It definitely didn’t come natural to me and it was a lot of work to exclusively nurse (no bottles)/pump for 2+ years and work full time. I was grateful for summer breaks, my workhorse pump, and my very supportive colleagues.