Soapwort

The plant variety that produces double flowers is Saponaria ‘Flora Pleno’, which is pale pink and white with a delicate scent. 

Common names are soapwort and “bouncing bet.” The plant spreads a lot, as it will grow almost anywhere and is often found along railroad tracks and even in dust heaps. In gardens, it is best confined to the outskirts not the main flower borders. My advice is that it is best grown only in pots.