Using this indorex stuff

[LanguidLobster]

It doesn't actually say on the can that it needs to be washed off afterwards, but also says to spray on soft furnishings.

What?? It's confusing me

I have used this I didn't wash it off anywhere. Not sure I understand what you are asking.

Oh, I'm mentally struggling with the idea of spraying on a chemical and then just leaving it.

I guess if that's what you do then that's what you do, seems a bizarre concept to me. The fleas liked a woollen blanket so I'm steeling myself to spray it and not have to wash it out, mental block basically

It protects for fleas for around six months or something, that's why it needs to stay and not be washed. However, mostly they mean things that you couldn't wash anyway like rugs and carpets, armchairs and sofas, fabric lampshades, mattresses... Your bedding and pet bedding should be washed of course.

We had to use it. You're meant to hoover carpets after. But leave anything else. It works well though. Last summer my legs were covered in bites. None this year.

Wash you blanket in the machine at 40degrees and that will kill any larvae and no need to spray.
The point of indorex is that you leave it on the carpet and furnishings and it continues to inhibit larvae development for a year.