The curved surface sliders or Friction Isolation Pendula (FIP) are sliding isolators based on the working principle of the simple pendulum. In a structure that is isolated by means of curved surface sliders, the period of oscillation mainly depends on the radius of curvature of the curved sliding surface, i.e. it is almost independent from the mass of the structure. The Friction Isolation Pendulum can be designed and manufactured in two main types, with one or two primary spherical sliding surfaces that accomodates the horizontal displacement, respectively classified as FIP or FIP-D series. The FIP series devices are characterised by: i) a concave slider (top element in the picture) whose radius of curvature imposes the period of oscillation and that accomodates for the horizontal displacement; ii) a base element with a secondary concave sliding surface that permits the rotation; iii) a steel intermediate element with two convex surfaces suitably shaped to be coupled with the other two elements. The device can also be installed upside-down, i.e. with the main concave slider at the bottom.The FIP-D series or double concave curved surface sliders are characterised by two primary concave sliding surfaces with the same radius of curvature; both surfaces accomodate for horizontal displacement and rotation.