Without seeing a photo, I’d guess it’s one of the usual suspects: teak, cedar, redwood, white oak, or pressure-treated pine. Higher-end benches are often teak or ipe. Teak is the gold standard because its natural oils and rubber make it highly resistant to water, rot, and insects. Cedar and redwood are lighter and cheaper, and they hold up well in rain because their natural tannins and oils slow decay. White oak is dense and less porous than red oak, so it sheds water better. Pressure-treated pine is common on budget benches; it can survive rain but tends to warp, crack, or check over time if not sealed.
Will it hold up in the rain? Yes, if it’s naturally weather-resistant or properly sealed. Rain alone won’t ruin a good bench overnight, but repeated wet-dry cycles are what cause cracking, cupping, and rot. Look for slatted seats so water drains off, stainless or galvanized hardware to avoid rust stains, and a fresh coat of exterior oil or sealant every year or two. If the bench sits in constant shade or collects leaves and dirt, trapped moisture will shorten its life faster than rain alone. For the best rainy-weather performance, teak, cedar, redwood, or ipe are your safest choices.