Spider silks are protein polymers with outstanding physical properties. A benchmark for spider silks is the dragline thread of the golden silk spider Nephila. Our study using urea super-contraction suggests a new model for the microstructure of this silk. According to this model, which challenges the general view, this silk consists of a structured fibril tube surrounding a thin core. This hypothetical structural organization could explain the supreme tensile strength of this interesting biopolymer.