Printed wiring board, printed circuit board, prepreg

A prepreg used as a material for a printed wiring board, the printed wiring board including:

• an inner insulating layer including a conductive wire;
• a first outermost insulating layer disposed on a first surface of the inner insulating layer;
• and a second outermost insulating layer disposed on a second surface of the inner insulating layer, wherein:
• a cured product of the prepreg constitutes each of the first outermost insulating layer and the second outermost insulating layer,
• each of the first outermost insulating layer and the second outermost insulating layer is a cured product of a prepreg, the prepreg including a thermosetting resin composition and a base material impregnated with the thermosetting resin composition,
• the thermosetting resin composition includes an elasticity lowering agent,
• the elasticity lowering agent includes at least one selected from the group consisting of ethylene-acrylic rubber including carboxyl group, nitrile rubber including carboxyl group, core-shell type rubber, acrylic rubber powers, and silicone powders,
• a bending elastic modulus of each of the first outermost insulating layer and the second outermost insulating layer ranges from ¼ to ¾, inclusive, of a bending elastic modulus of the inner insulating layer, and
• a glass transition temperature of each of the first outermost insulating layer and the second outermost insulating layer falls within ±20° C. of a glass transition temperature of the inner insulating layer.