Fractional B-splines Bσ, σ ≥ 1, are piecewise polynomials of fractional degree that interpolate the classical Schoenberg splines equation image, with respect to the degree. As the Schoenberg splines of order ≥ 3, they in general do not satisfy the interpolation property equation image. However, the application of the interpolation filter equation image—if well-defined—in the frequency domain yields a fundamental spline of fractional order that does satisfy the interpolation property. We extend these result via ridge functions to multivariate fractional B-splines.