Do us all a favour, ask her then tell us.. I've never come across the term before so maybe something is getting lost in translation?
Jay
She says that 'synthetic jacket' did mean condoms.
Reading everything back, I think her original sentence seemed to be in response to one of mine which said 'I will consider pretty much anything except hardsports and bareback' - so on balance I think she meant to say 'I also don't do hardsports and I always use condoms'.
Why bother making up some stupid euphemism and then using it so badly? She's English, incidentally, so she should be able to see that what she actually wrote was really confusing.
In any case, I shan't be seeing her. Thank you to everyone who replied.