This is an Old Navy top that I'm calling the Flutter Sleeve Plaid Top (item #653504). I could not find this top online - not when I initially tried it on, nor now. The top is alpha-sized, and retailed for $19.50. It might have been a cotton/linen blend, but I'm not positive. Either way, the fabric is smooth, and is light-medium weight.
I thought this top was pretty cute. I think the sleeves really won me over, because I think they elevate the top from just being another sleeveless top. I also think this piece would work really well as a both a standalone and layering piece. However,I wasn't really looking to buy the day I tried this on, so I left this one behind.