I know this isn't what you asked, but I'm gonna post it anyway............I changed to an Under Armor heat gear shirt a few years back and it's been amazing. It's a short sleeve compression shirt (so it's super-thin and tight, but stretchy). I hated how regular undershirts would bunch up or feel bulky under a regular shirt. This one is skin-tight, so it doesn't bunch up, but it's so thin and light that it feels like not wearing one at all. And because it's stretchy, it stays tucked in.
They're expensive, as undershirts go, at about $20-25 each, but they're worth it. I have a couple of them. I wear the same one 2-3 days in a row (if I'm just sitting at a desk not sweating), then alternate for a couple of days.
I don't wear the compression except in winter with the Cold Gear, but I have a bunch of different "performance" shirts including UA, Adidas and cheapos. They're all IMO solid for undershirts under a pullover polo or button-down.
They're great for traveling because if you're not sweating then you can wear it more than once. If you do, wash it out in the bathtub, wring it and hang it. Lightweight and great for packing. When I fly, I usually toss one into my backpack (along with a toothbrush) just in case.
