I have heard that if you are wearing somebody elses Talit you don’t say the bracha when putting it on is this true? If it is why, surely its the same item and your putting it on for the same purpose no matter who it belongs to so why say a bracha if its yours but not if your borrowing it from somebody else?

The Torah specifies that the Mitzva of Tzitzit is on "Bigdeichem" - your garments. On a borrowed garment one is exempt from the Mitzvah and may wear the garment without Tzitzit for up to 30 days. Nevertheless, the Shulchan Aruch says that if one borrows a Tallit, one may say a Bracha. The explanation is that since the lender wants the borrower to fulfill the Mitzvah, he will intend to transfer ownership of the Tallit for the duration of the loan (even if the lender doesn't know, presumably he would agree, so there is an implicit transfer in any case). The Mishna Brura says it is best when borrowing a Tallit to have intention not to aquire the Tallit and not to make a Bracha, in order not to rely upon the implied Kinyan (transfer).