Product review (1 stars): Hope you don't need--- all--- of the minus 8 foot duct ?
As another reviewer stated when pipe was fully stretched by it came to a little over 7 feet.  That was critical as my distance needed was eight feet as my duct joins at the ceiling so we needed to go  buy a short length of  metal pipe to make the  8 feet.  At over a dollar a foot for alum/ flex vinyl , i would at least expect to be not shortchanged  as first few inches at each end are not usable from poor cutting at factory and then you don't even get the 8 feet you paid for.  The package it came in had a zip tie to keep it compressed so I don't think someone would chop off a foot of pipe and zip tie it up again.