The Rongrein or 'RR' variety is one of the best Rambutan varieties sought for it's sweetness, long shelf life and 'tuklapin' aspect.
RR Rambutan's are already sweet even when the hair follicles are still green/red (hence they long shelf life). They get even sweeter and juicier as they ripen.
Once Ripe (all follicles turn red) Rambutan's over-mature quickly (follicles turn brown) so refrigerate Rambutan's once they're matured.
Locally, Rambutan's are either 'Supsupin' or 'Tuklapin'. Supsupin varieties have the meat attached to the seed making you suck-on or 'supsup'. Tuklapin varieties are preferred because the rambutan meat easily separates from the seed making for a better eating experience.