The phrase "weight percent" refers to the proportion or amount of a substance present in a mixture or compound, expressed as a percentage of its weight. Full definition
And 50 weight percent appears to be the magic number. (sciencedaily.com)
This isn't a perfect system, because I'm abusing the notion of «weighted percent errors» a little here, but hopefully the idea is clear. (money.stackexchange.com)
«But we got our membrane to 50 weight percent without compromising its structural integrity,» says Su. (sciencedaily.com)