one type of quilt that does this is a bargello and if you search for that word here on the board you'll find a lot of information plus you can google it on the web and find a lot. Another type of tube quilt is demonstrated by the Missouri Star Quilt Company, and others, even links on the board...but their technique doesn't require you to open any seams, it's a way to cut tubes to make blocks easily. Again, check out this board for Missouri Star Quilt links or go check them out on the web. They also have lots of other good tutorials.