This is a water proof sweater, because it's made of lanolin. Click on this image to make it larger. You really need to see the details to understand the significance of the pattern. Rick bought this sweater from a woman in a one-and-a-half story cottage on Aran Island when he was sixteen. It was white then.
According to Rick, all of the families on the island have their own pattern. The fishermen wear these sweaters to sea, and if they shipwreck, they can be identified by their family's pattern. The central pop-corn panel represents a field and the hope that it will end up being full. The diamonds represent nets for industry and enterprise. These nets are empty, signifying that the family is not wealthy. The cables separating the panels represent strength and steadfastness.
I found a site (clanarans.com) that sells Aran Island sweaters and it looks to me like this one is from the Murphy Clan. If you have an Irish last name (I don't) you can look up your family's pattern on the site. It's exciting that a sweater can have so much cultural significance.