There is described a method for forming tubular lengths of web material, comprising the steps of a) winding a linear portion (2) of web material in a tubular configuration such that opposite vertical ends (34) of said linear portion (2) overlap; and b) welding the overlapping ends (2) to fix the linear portion (2) of web material in sleeve configuration; step b) comprising the steps of c) heating up to a first temperature (T1) a first region (R') of the linear portion (2) over the whole of which said ends (34) overlap; and d) heating up to a second temperature (T2) lower than the first temperature (T1) a second region (R") of the linear portion (2) substantially adjacent to the first region (R'), the ends (34) of the portion (2) of labelling web material overlapping over only a part of the second region (R").