Early after surgery, one side can be more swollen than the other, making it feel firmer. I tell our patients the one thing we can guarantee is that two-sided procedures always heal differently.I also feel a difference when one breast is smaller than the other, and a larger implant is placed into the smaller breast, resulting in a tighter fit. Another reason one side may feel firmer is if the firmer breast is developing a capsular contracture, in which the scar around the implant (called a capsule) shrinks and squeezes on the implant, making it feel firmer.See your plastic surgeon to find out what he/she thinks might be causing the difference.
It is difficult to attempt answer your question without a photograph. It is very common for implants to feel different on either side in the early stages of recovery. One breast may be adjusting to the implant more quickly than the other and if one side is particularly tight the implant may feel more palpable.Usually these asymmetries resolve over the course of 6-8 weeks. However I suggest that you see your plastic surgeon for an examination and discussion of what may be causing this asymmetry.