The top layer of 0/3 baby mattress composed of layers of form and double-sided. The core layer composed of high density of spring coils which have been treated with special process. The mattress is designed according to ergonomic nature of human sleeping posture. Slightly dented (within 1 inch) on the sleeping area is the result of pressure and mild re-bounce on the layers to suit the body curve, and thus giving the most comfortable support to baby. Slightly dent is normal and it is not malfunction of the spring coils. After 3 months of first using, we recommend to turn the mattress to opposite direction, and then do it again after every 4 weeks. Your mattress will then be kept in its best support by letting the pressure spreading evenly periodically.