i have used fusable batting a couple times, really don't like it. it's ok for purses/totes i guess and probably wall hangings. yes it will (plump-up) a little bit when it is washed. i do not know if there are a lot of different fusable batts but the one i used was about the same weight/density as dream poly, or hobbs select 80/20. i would think that it would be fine to use something different in the borders. i have successfully used 2 and 3 different battings in the same project. you only have to watch for washing and quilting requirements (as in does it have to be quilted every 2" or every 10" and is one cold water only, ect. as long as the properties work together it will not be a problem.