Now, as to what the Egyptians wore exactly, let’s first take a look at when the Jews were in Egypt. The Jewish Time Line Encyclopedia by Rabbi Mattis Kantor (order at http://store.yahoo.com/eichlers/876682298.html) places the Jews’ relocation to Egypt in 1523 BCE, the youth of the New Kingdom (1570-1075 BCE). So, what were the Egyptians wearing in the New Kingdom? Very little. Egypt is a hot country to this day—up to 108 degrees in the summer in some areas—with very little rain and certainly little cold to worry about. Thus, a lot of clothing to protect one from the elements was unnecessary. The ancient Egyptians wore as little as possible due to the heat—and due to their depraved beliefs. And what they did wear was almost always light and airy. With the advent of the New Kingdom, Egyptian clothing — particularly women’s clothing — took a downward turn to even skimpier fare.

Men, especially the working class, generally wore nothing more than reed sandals and kilts (skirts worn by men), and often wore nothing. Noblemen would occasionally wear tunics, cloaks, or robes, though. Women, who mostly stayed indoors, would likewise wear little clothing, if any (although they had remarkably advanced jewelry, cosmetics, hygiene and skin care).

The picture that emerges is thus one of shocking nudity by today’s standards. Into this society entered Jacob and his family — a clan of 70 individuals — who, as the midrash tells us, observed the Torah even before it was given. This observance included the laws of tzniut — modesty, and thus, in response to your question, the answer is: we don’t know. We cannot know exactly what the Jews’ clothing looked like — what color, style, design or weave they consisted of — but what we do know is that they did NOT wear Egyptian clothing because it was a radical violation of tzniut. Wearing Egyptian clothing would have entailed walking around mostly if not totally undressed most of the day. Because the Jews observed tzniut more or less the way it is today, we can say with certainty that the Jewish women’s clothing covered the body from the neck to the knees (right and left, front and back, unlike the Egyptians), and from the shoulders to the elbows, in contrast to Egyptian women, who did not. The Jewish men, in contrast to their Egyptian counterparts, did not go bare-chested and certainly not exposed below the waist. Shoes were non-existent; it was not considered immodest by the Jews or Egyptians to go barefoot, although sandals were used.

So it’s not so much that the Jews wore Style A while the Egyptians wore Style B — it is, rather, that the Jews wore decent clothing while the Egyptians did not. And as per the wording of your question—“…before they became slaves,” they probably wore the same clothing as slaves that they wore before becoming slaves. Tzniut still applied during slavery, although it very well may be that as slavery worsened, especially towards the end of the Exile, the Jews were forced, upon pain of death, to violate their dress code.

Hope this helps!