Bringing home your new pet will be a very exciting experience, but some patience should be exercised, and preparation undergone, to ensure that the animal will thrive.
Most likely your betta will be travelling from the pet store or rescue in a small container or bag. The smaller the volume of water, the more susceptible it is to rapid temperature changes (influenced by the temperature outside the container).
As you may be travelling home during the winter, in a cold vehicle, possibly over significant distance, it may be best to put the fish's bag/container in a small cooler or insulated lunch bag (with no ice in it, nor any heating packs, of course!) for the journey. This will offer extra insulation against temperature fluctuations, which, if sudden, are very stressful to fish, in severe cases causing shock or even death. The idea is simply to maintain the temperature of the water that the fish is in as best as possible, not to alter it in any way with the cooler.
Please note that while a betta, as a less delicate variety of fish, may survive a trip home without the insulation of a cooler, this does not make the trip any less stressful for them. Simply because they could withstand the trip without extra precautions, and because they cannot vocally communicate their distress to you, these are not reasons that they should be denied extra efforts to preserve their health.
Acclimation is the process of transitioning a fish from the water in which s/he lived previously (ie: at the pet store) to the water in your tank. These two waters may differ significantly on several parameters, including temperature and pH, and so this transition must be done slowly so as not to shock the fish and jeopardize his/her health.
Bettas have the same acclimation requirements as other tropical fish - the DRIP ACCLIMATION method may be the best (see our page for the procedure), but any method must allow the fish to gradually adjust to the water chemistry and temperature of their new tank water prior to immersion/release into it.
When first introduced into their new tank, naturally bettas may experience some stress and may not eat for the first few days (see the end of the FEEDING section for a further discussion of this). To help a stressed betta to relax, lights can be dimmed and the tank can be placed with it's back near a wall so that the betta is not dealing with your movement on all sides of his tank and can feel more secure. Boxes, etc. can also be stood next to the sides of the tank if the fish seems extra stressed, so as to block out movement on the sides of the tank as well. Signs of stress include pale coloration, clamped fins, and hiding in the tank. These symptoms should resolve in a few days as the fish becomes comfortable in their new home and begins to explore. However, if the fish is still showing signs of stress after a few days, this may signify something more serious, such as illness, and should be monitored.