If you're wanting to fly thermal, don't go foam for your first choice unless you don't want to have much success.

Thermal success with a sailplane smaller than about 2meters is not easy. Some days all you'll get is landing practice with the small birds. And they don't make too many foam sailplanes that're large enough to be much help catching lift. The odds on catching usable lift go up with wingspan. And there's a point where the odds turn against you pretty strongly and it's right around 2m and smaller.

Want proof. Go fly a thermal contest. Watch how the Unlimiteds work. That class trophy often comes down to landing points and a fair number of the entrants go most of the rounds. Watch how the 2m class winds up going to the only guy who maxed out all the flights. Often the winner is the guy who made the longest time the last round. It's harder to make long flights with the smaller gliders. They can't hunt as long, and don't eat up good air as well.