Do skin tightening treatments (like Ultherapy or RFs) work better on less “fibrous” areas?

No, this won't make ultherapy less effective. Non surgical options give only mild improvement compared to a hi definition procedure. A hi definition liposuction like a VASER HI DEF revision combined with ThermiRF which can be performed at the same time as a thigh lift if you're a candidate, would give the most improvement. Other options for skin tightening would be a combination approach with vanquish, venus legacy, exilis, celllutone/Zwave. I recommend getting a formal evaluation with a high definition physique expert. Best, Dr. Emer

The ultherapy and other energy based treatments work by by heating underlying tissues, causing collagen breakdown, remodeling and subsequent tightening over time. The cellulite should not affect efficacy of the treatments but theoretically can affect the amount of tightening you can get. Bottom line is that having cellulite is not a consideration in whether the ultherapy will work

Thanks for your question and as always we recommend that you have a consultation with a board certified dermatologist or plastic surgeon to learn all the best treatment options for you and your concern.  Ultherapy works on lax skin as does most of the RF skin tightening devices out there.  You need to have a complete examination by someone who knows what they are doing to determine if you are an appropriate candidate for the areas of concern and you must realize that treatment and maintenance are needed.  Find the right provider in your area and you will do well.