Toddy's got it right. At home one rinses the rice, adds and equal amount of rice to cold water and then brings it to a boil. Once boiling one turns the heat down to the absolute minimum for a few minutes and when the water has evaporated one turns it off and leave it to sit for about ten to fifteen minutes. This is how most Asian cooks would cook standard white rice.
If they use a recipe that involves using boiling water straight onto the rice then they leave it to stand in cold water for about an hour first. Then they drain it for about twenty minutes. Next they sauté it in ghee, butter or oil, add the boiling water and bring it back to the boil before turning off the heat and leaving it to sit
For your vacuum flask technique I reckon you'd do it like this: First you need to have at least as much water as rice, possibly more. You need to leave it to stand for at least 20 minutes in the flask IMO. Quick cook rice or parboiled rice has the most chance of success because it's been partially cooked already. Wholegrain rice wouldn't work at all.
Might be better to cook the rice at home first. Leave it too cool, wrap it in plastic and take it with you. Then, when you are ready to eat it put it in the flask and the hot water will heat it up for you.