cumulative adjectives Two or more adjectives that do not modify a noun equally. Instead, one or two of the adjectives closest to the noun form a noun phrase that the remaining adjectives modify: colorful hot-air balloons.
Leather modifies sandals, and soft modifies leather sandals as a unit. Thus the meaning is cumulative, and a comma would interrupt the connection between the adjectives and the noun. (See P1-i to review the use of commas with coordinate adjectives.)