Explanation #1: This implies that something that is hard is not subject to Kil'ayim.

Precedent: And this is also implied in Yoma (Daf 69. & 69:), where the Gemara relates how the Kohanim would place their folded clothes under their heads, and promptly asks why this was not Kil'ayim.

Precedent (cont.): The Gemara there follows the same pattern as it does here. And Rav Ashi ultimately answers that the Bigdei Kehunah are hard.

(The Sugya in Erchin) Question: The Gemara in Erchin (Daf 3:) queries the ruling that everyone is Chayav to wear Tzitzis, Kohanim, Levi'im and Yisre'elim 'But is this not obvious? Is it because they are Kohanim that they should be Patur?"

Answer: We would have otherwise thought that, due to the juxtaposition of the Pesukim "Lo Silbash Sha'atnez" and "Gedilim Ta'aseh lach", whoever is subject to the Isur of Sha'atnez is Chayav Tzitzis, and Kohanim, who are permitted to wear Sha'tnez (in the Bigdei Kehunah) are therefore Patur from Tzitzis.

Question: What is he Sugya there saying, seeing as Kil'ayim is permitted by the Kohanim, whose clothes are hard?

Answer. Explanation #2: It therefore seems that it is only spreading hard clothes beneath oneself that is permitted, since even by soft clothes this is only de'Rabbanan, so by hard clothes they did not decree.

Explanation #2 (cont.): And the Gemara cites the case of the hard furs of Neiresh, which were permitted to spread underneath oneself (as Rashi explains).

Opinion #1: But soft ones are forbidden, as the Gemara says there 'Furs are forbidden, because they have been carded (pressed together)'.

Refutation: But this does not appear correct, seeing as 'permitted' implies even to wear.

Opinion #2: It is therefore correct to say that they (the hard furs) are even permitted to wear.

Question: Why does the Gemara cite the case of Gamda de'Neiresh, seeing as Tosfos explained earlier that hard Kil'ayim is permitted only to lie on, but not to wear?

Answer: Regarding the case of Bigdei Kehunah speaks where they are 'Shu'a Tavuy ve'Nuz', in which case it is Sha'atnez mi'd'Oraysa, and since they are Asur min ha'Torah, even when they are hard, they may not be worn or draped over oneself ...

Answer (cont.): Whereas Gamda de'Neresh is only Asur mi'de'Rabbanan, as the Gemara says in Nidah (Daf 61:), since mi'd'Oraysa it needs to be Shu'a Tavuy ve'Nuz.

Implied Question: And when the Gemara declares felt-cloaks Asur ...

Answer: That is only mi'de'Rabbanan.

Conclusion: Consequently, since the Isur on soft ones even regarding wearing, is only mi'de'Rabbanan, the Rabbanan did not decree on hard ones.

Implied Question: And as for those shoe-socks that are called in German "gemeils" that we wear that sometimes contain wool ...

Answer: Since it is possible to make a small tear and remove the wool via the hole, since one is merely held by the other, it is permitted.

Conclusion: If however, they would place small pieces of woolen cloth inside, it would certainly be forbidden.

Clarification: This come to include Tefilin, which one may send, seeing as there is no Isur of wearing them (on Shabbos and Yom-Tov).

Refuted Explanation: It is not however, coming to permit a Sandal ha'Mesumar, which one may definitely not send ...

Refutation: Because if one allows sending it, one will come to wear it, which is in fact Asur.

Conclusion: But Tefilin (even though Shabbos and Yom-Tov are not a time to wear Tefilin) nevertheless there is no prohibition against doing so.

Explanation #1: Rashi explains that both cases speak on Erev Shabbos, since 'Shabbos is not a time to wear Tefilin'.

Question: In that case, why does the Tana mention 'and the sun set' with regard to the case of 'Ba ba'Derech', and by 'Yoshev be'Veis-ha'Medrash', he mentions 've'Kidesh ha'Yom', seeing as the same reason applies to both of them (Why did he change the Lashon from one to the other)?

Explanation #2: One therefore needs to explain that 'Ba ba'Derech ve'Shak'ah ... ' is speaking on a weekday, because once the sun sets, one is obligated to remove one's Tefilin, and the Tana is coming to teach us that 'Nighttime is not a time to wear Tefilin'.

Question: In that case, one may well ask, why can one not simply carry the Tefilin in one's hands?

Answer: Because he may drop them.

Explanation #2 (concl): Whereas in the case of 'Yoshev be'Veis-ha'Medrash' he mentions 've'Kidesh ha'Yom', because it is speaking on Erev Shabbos, and the Tana is coming to teach us that 'Shabbos is not a time to wear Tefilin'.

Implied Question: Even though earlier he said to his Talmidim to 'Eat nice foods and drink sweet drinks?

Answer: This was because he had finished the D'rashah.

Conclusion: On other days too, they would eat after the D'rashah ...

Conclusion (cont.): Nevertheless, he told them to eat ... and drink ... , on account of Simchas Yom-Tov.

Implied Question: And when the Gemara says in Pesachim (Daf 112.) 'Rather make your Shabbos a weekday than borrow from others' ...

Answer: It speaks where he does not have the means to repay the debt (See Hagahos ve'Tziyunim & Hagahos ha'G'ra).