Acrylic both Marbled and "stone like" surfaces; Acrylic spas are for the most part backed by a fiberglass compound, and while bonding resins (the stuff that keeps the acrylic and fiberglass stuck together) have improved in recent years, acrylic spas backed by fiberglass, are prone to "delaminating" where the surface material and the fiberglass separate and cause unsightly bubbles. It is important when purchasing a tub like this to look at the "Surface Warranty" and not the structural shell warranty. These two are usually separated in the warranty coverage. It is also important to purchase a spa from a manufacturer that has been around a while. After a company goes out of business, in most places their warranty cannot be enforced. So a 100-year warranty that was issued by a company that is only around 6 months is not much use.