Sforno on Exodus 35:26/ספורנו על שמות ל״ה:כ״ו

1טוו את העזים, while the wool was still on the goats, as per Shabbat 99. The reason was to lend an additional sheen to the yarn spun from this hair. There are many materials which suffer a reduction in appearance once they are separated from their original habitat. We all are aware of this phenomenon with bees’ honey. [The author cites other examples of a similar nature occurring with products that I am not familiar with. Ed.]