Will 400cc, dual plane implants still look natural as I don't want to go too big? (Photos)

That implant size may look very nice on you. It is important that you feel comfortable and confident in your surgical plan. I encourage you to return to your surgeon's office to discuss any concerns you have. Many surgeons have sample implants you can "try on" to get an idea of how you may look after surgery.

Thanks for including your Crisalix 'before photos' - you appear to have a moderately wide breast foot print and a fair amount of your own breast tissue. a 400 cc moderate profile implant might look very nice on you. It's impossible to say how 'natural' your post op result will be, as this is a subjective descriptor.