What to Bring
Unlike triathlon, yoga is a low-gear activity. No special watches measuring aura levels or custom fit footwear for chakra grounding, just a mat. Most yoga studios will have mats available to rent for a few dollars but your own yoga mat is worth the investment monetarily and hygienically. You are going to spend an hour standing, sitting or splayed out face down on that mat and although good studios clean mats between uses, having your own ensures you spend savasana laying in a pool of only your own sweat. In addition to your mat, plan to bring a small towel and a water bottle. Like mats, towels can be rented at most studios if you forget.
There are many options for yoga mats. I personally have a Manduka but there are numerous choices for every price point.
Manduka mats are heavier than most but I have found they are the best for grip when things pick up in a heated class. Maduka mats have a lifetime guarantee and come in longer sizes for tall yogis.
Jade mats are very popular, eco friendly, sturdy and light. An excellent choice.
Lulu Lemmon mats have a bit more cushion and are good for gripping. They are antimicrobial, so you won't worry about unrolling a moldy mat.
Gaiam, a personal favorite for an inexpensive or travel yoga mat. A Gaiam mat can easily be purchased at Target or Amazon for around $20. No frills but it will serve you well.
Avoid Pilates or workout mats, they are thicker than yoga mats and will make balancing far more difficult.
If you are going to a heated class or you just sweat a great deal you may also want to consider a yogi toes mat towel. It will help you maintain traction as a puddle of water accumulates on your mat and the rubber grips on the bottom prevent the towel from sliding. Also to consider, bike gloves. They provide a tiny bit of padding and some extra traction for sweaty palms.
USAT rules state that you are not permitted to be naked in transition, the same rules apply to a yoga studio. If it is a heated vinyasa, power yoga or bikram class, it is going to get very warm...extremely warm. In a heated class it is not uncommon for men to practice shirtless and women to practice in a sports bra-type top. In non-heated classes people typically wear shirts. When picking your ensemble ask yourself, would I feel comfortable wearing this outfit upside down? Loose fitting shirts, shorts and pants will slide up your legs or torso in downward facing dog and may reveal more than you intended to your fellow yogis. Fitted yoga pants and tops are easily available at yoga stores like Lulu Lemmon, Lucy and Athleta. As a triathlete, you already own a host of fitted wicking clothing. Run shorts, tri shorts and tops are fine if you want to avoid acquiring more sports gear.
There are two kinds of tri people, those who waste time in transition putting on socks and the rest of us who actually want to race. In yoga you can usually find one adamant sock wearer in a class but I assure you, you will look cooler and have an easier time with the poses if you skip the socks and embrace bare feet.
Types of Yoga
We have an inappropriate number of options in triathlon: Olympic or Full, Ironman or Rev 3, TT bike or Road? Yoga also presents options of style, something for everyone.
Vinyasa Flow combines movement with breathe, with each postures flowing into the next. There is no set series of postures, so classes vary and teachers often take requests for certain postures and parts of the body for the focus of the class (hip openers, shoulders, hamstrings). Full disclosures, I'm a vinyasa teacher.
Ashtunga yoga is known for its athletic style and broken down into four series. The first or primary series is made up of 75 specific yoga postures.
Anusara yoga is known for it's lively themes and strong heart opening.
Iyengar yoga has a strong focus on alignment. Yoga props are used to ensure students are aligned properly in each pose.
Bikram yoga is practiced in a 105 degree room with 40% humidity. Every Bikram class is made up of the same 26 postures with a strong focus on alignment.
Hatha yoga's hallmark is slow and gentle movement combined with breathe. Looking for a relaxing class- head to Hatha.
Most studios break down the classes by levels and often include beginner classes into their schedules. If you are completely new to yoga make the beginner or level 1 class your first stop. Yes, you are an athlete and I'm sure you are very strong with endurance for days but level 1.5 or yoga classes are for experienced students and teachers rarely give directions for the basic postures. Ensuring you have a base of knowledge and an understanding of the basic postures will make class far more interesting.
Talk to your yoga teacher
I know you were expecting someone called Moon Goddess who only eats raw foods and spends weekends playing the yute. It's DC, your yoga teacher is most likely a State Department lawyer from New Jersey with the twitter handle: DCYogaPolitico, she is not to be feared. A good teacher will introduce themselves to students and inquire about injuries but if they do not, be bold and introduce yourself and let them know you are new. You are a triathlete, I'm sure you have a host of injuries miles long with MRIs and scars to prove it. Tell your yoga teacher anything pertinent, especially knee, neck and back injuries. The teacher is not a medical expert but they can tell you which postures to avoid and how to make adjustments in postures.
Namaste and best wishes for an amazing yoga class