I'm not sure what the RDT stands for in The North Face's line of RDT garments, but I'm pretty sure I've narrowed it down to "Remain Drier Throughout." (Or maybe "Really Delicious Taste"). The Women's L/S RDT V-Neck is made of a recycled polyester knit with FlashDry™ fibers to improve dry times and wick moisture away from your skin. The seams are flatlock to lay flat so they won't irritate your skin on long runs. 100% geared towards keeping you comfortable.
ps- I just tasted one.. RDT certainly does not mean "Really Delicious Taste."