Japanese Bath Tubs
Neptune was the first manufacture that was able to make these japanese-inspired bathtubs from a solid sheet of Acrylic. For other manufactures it was just to difficult to mold a sheet of acrylic in that deep of tub, even today there are very few tubs that are this deep that are made from acrylic.
Benefits of Acrylic
Acrylic tubs are nonporous,this makes them easier to clean and repair, this also meas that they can not mold or mildew. Acrylic tubs are made of a solid surface material, which means they will not fade over time. If acrylic somehow gets damaged, it can easily be repaired, and you will never see the damaged area. It's a long-lasting option for a tub, likely to be useful for 30 years and beyond.