I’m not sure if these will run the same way, but when I’ve gotten zorrel shirts from woot, they seem to shrink an incredible amount. I bought 4x so they would be over-sized and I had room for them to shrink a little in the dryer. They shrunk down to about 2x size in one wash / dry. I might suggest that you order big.
As opposed to indoor polo shirts?
Only so-so reviews on Amazon, including comments that the shirts run small, the cotton shirts feel scratchy (presumably from the treatment?), and, from one reviewer, can possibly cause a rash if worn many days in a row.
http://www.amazon.com/Zorrel-Insect-Shield-Apparel-Womens/dp/B002FU6SQS
http://www.amazon.com/Zorrel-Insect-Shield-Apparel-Sonoma/dp/B002FU6RQ4
Here’s Zorrel’s info page: https://www.zorrel.com/catalog/?cid=4
And a previous sale here on woot!: http://accessories.woot.com/forums/viewpost.aspx?postid=6289087&ref=cnt_odet_jtd