If you made the tube by sweeping a profile along a path... I would suggest adding a loft to the end of the "tube" & loft it to a "compressed" profile.
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but how can I make a loft that is not filled in the middle. I can select two regions(the pipe) to make the loft, but when actually creating the loft, solidworks gives an error.
You can always do a Shell after the loft, or
Create inner & outer start & finish profiles of the pipe, & loft between those, or
Create a solid sweep & loft first, then do a shell on both.
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