This product is not tested specifically for use with fibroblasts, but has been used successfully by other researchers. While optimization may be required, the suggested working concentration for this material is 5 ug to 10ug per ml of medium.
Please see the links below to review several publications that may be of interest:
https://www.sigmaaldrich.com/catalog/papers/20336525
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3456965/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3055793/
http://www.sussex.ac.uk/gdsc/intranet/pdfs/Lentiviral_Primary_Fibroblast_Immortalisation_(hTERTing).pdf