Multi-piece solid golf ball

A multi-piece solid golf ball comprising a core, an envelope layer encasing the core, an intermediate layer encasing the envelope layer, and a cover which encases the intermediate layer and has formed on a surface thereof a plurality of dimples, wherein the envelope layer consists of an inner envelope layer, an intermediate envelope layer and an outer envelope layer, such that the total number of layers in the multi-piece solid golf ball is six;

• the inner, intermediate and outer envelope layers, the intermediate layer and the cover are each formed primarily of a resin material which may be of the same or different types;
• the core is formed primarily of a rubber material;
• the cover has a material hardness (Shore D) which is higher than a core center hardness (Shore D);
• and one of the inner layers has a material hardness (Shore D) which is higher than either or both of the cover material hardness (Shore D) and the average core hardness (defined as the arithmetic mean of the core surface hardness and the core center hardness),
• wherein the intermediate envelope layer is formed so as to be harder than the inner envelope layer and to have a material hardness difference (Shore D) with the inner envelope layer of from 1 to 4, and so as to be softer than the outer envelope layer and to have a material hardness difference (Shore D) with the outer envelope layer of from 1 to 4,
• wherein the inner envelope layer, intermediate envelope layer and outer envelope layer have thicknesses which satisfy the following relationship:
• inner envelope layer thickness>intermediate envelope thickness>outer envelope layer thickness, and
• wherein the ratios (intermediate envelope layer thickness)/(outer envelope layer thickness) and (inner envelope layer thickness)/(intermediate envelope layer thickness) are each at least 1.1.