Might be TMI, but I recently bought a multipack of M&S knickers, I have had them before, and the new pack said "new and improved fabric" - immediately got me suspicious, but I need new knickers, so I bought them anyway. The original ones were cotton, the new ones I think have some Lycra in the cotton. They feel fine, but then I get my period and I get a few stains on them. Normally they wash very well, even period stains comes out with biological washing powder. But not these new ones! So after washing them I soak them in a hot water and biological washing powder solution over night and wash them again. Stains are still there, and it's like they are raised! Any tips?