The present invention has an object to provide (i) a nonaqueous electrolyte secondary battery separator having excellent ion permeability and (ii) an insulating porous layer by which to achieve the nonaqueous electrolyte secondary battery separator. The insulating porous layer is a nonaqueous electrolyte secondary battery insulating porous layer containing: a resin A; and a resin B, the resin A and the resin B having therebetween a Hansen solubility parameter distance (HSP distance) (Ra) of not more than 10 MPa1/2.