I got some sort of welt/blister combination from the “stay put” silicon lining of a bra yesterday. I’ve never worn that bra for an “all day” scenario before – it’s a convertible type, and I’ve only ever used it under halter tops before, and hence, only for a few hours in an evening rather than almost 12 hours. I’ve never had that sort of problem before, certainly not that I recall with my other strapless and convertible bras.
It’s probably a combination of the silicon lines of that bra and the mid-90s heat that we’ve been dealing with here. I don’t like it much when things get this warm, I tend to sweat in this sort of heat, which probably enabled the bra to slide around a little bit and irritated the skin.