Content of b2b varies greatly between providers
At it's best the girl will be fully naked, then apply plenty of oil to both of you and then climb on top and glide her body all over your back, and then repeat on your front. She will use combinations of her arms, legs, body, ass, boobs, pussy
At it's worst the girl may go topless and rub her boobs on your back for a few minutes
My experience of soapy massage is closer to the best of b2b, but instead of oil the girl will use soapy water, and most times on an inflatable mattress on the floor. The soapy water needs to be repeatedly applied to maintain the slippiness
Nuru massage exchanges the soapy water of an ultra slippy Nuru gel (I think made from seaweed extract). The gel stays slippy far longer than soapy water so typically there's less stop and start to re-apply
All of my Soapy and Nuru massages have taken place at Soft Touch in Northampton, but I know there are other providers like Bubbles Spa in Nottingham. Other members here may be able to fill in the missing information