I just stumbled across the term soft swap in a post in r/polyamory and after some googling, I found I was intrigued. Having full-on sex with my partner and another person always seemed like to big a leap but oral sounds like a great way to dip the toe in.

I have a question, though: What is the general consensus about interaction between the partners? Is penetration generally allowed between established partners or does everyone agree to keep things oral? Is this different for threesome vs. foursome constellations?

I know that, in the end, it's all down to the boundaries you negotiate with play partners but I'm just curious what people's experiences and thoughts are. For instance, if I'm sharing my (female) partner with another man, would it create a strange dynamic if they could only do oral whereas we can also have penetrative sex? Does it affect the group dynamic of a foursome if everyone eventually ends up having penetrative sex with their partners?

Curious to hear about your thoughts & experiences!

TL;DR: Is it customary to have penetrative sex with your own partner during a threesome/foursome soft swap?