I’ve got most every piece of bodywork known to karting, and there have been some very light and flimsy plastic as well as some pretty beefy pieces in past years, but most of the newer karts have pretty lightweight plastic.
KarTechna, Birel (Riccardio) and TonyKart (FA/Kosmic) bodywork is probably the lightest (in that order), but CRG, Praga, TopKart, ItalKart (& more) are very, very close, I think it’s more about looks and durability than anything else at this point, unless you’re looking for a few ounces.
Post the brand of bodywork you currently have and what you’re looking at, and I’ll weigh them both.