I have a friend who is doing a major renovation of a commercial space. The contractor has installed flex for all the take-offs. The flex ranges from what looks like 8" diameter up to 16" diameter. The runs of the flex look like between 15 and 20 feet each where roughly half of that is horizontal then there is what looks like 2" fiber cloth straps that hold the duct where it drop 90 degrees down to where the outlets will be. I told him these sharp 90 degree bends are restricting the air flow significantly and he should talk to the contractor. I saw him today and said I bet the conversation went like this: "a friend told me this what do you think, and the reply would be your friend does not know what he is talking about". He said yup he asked both the contractor and the architect and both said I am wrong. So, what do you pro's think, is this acceptable or should he insist that they install galvanized elbows where they make these 90 pinch turns in the flex or some other option. Thanks for your input.