That One Should Not Bless When One's Limbs See [One's] Nakedness (i.e. Genitalia), Containing 6 S'ifim
If one was sleeping naked with his cloth, he needs to press the cloth to his heart, and then he may recite [Sh'ma] because [when] one's heart sees one's nakedness (i.e. genitalia) it is forbidden. Rem"a: And the same rule applies if one's heart see one's fellow's nakedness (i.e. genitalia), it is forbidden (Tur)
One who washes naked in clear water and wants to drink should cover [themselves] with a garment below their heart in order that their heart should not see their nakedness (i.e. genitalia) when they bless. And [this is] specifically with a garment, but with [one's] hands it is not [considered] covered. Rem"a: And the same rule applies if one covers their head with their hands, it is not considered a covering for the head - see below Siman 91 (Terumat HaDeshen in the name of Or Zarua) And if the water is murky such that one's body parts cannot be seen in it, it is permitted to recite while they are in it, as long as there is not a bad smell. And if one's heart is not in the water, only above the water, [then] even in clear water it is permitted (D"A)
If a person hugs one's body with their arms, it is considered a separation [between the heart and genitalia].
There is [an authority] who says that women can bless and pray when they are wearing a shirt, even though they it doesn't separate from below the heart. Rem"a: And if they are naked, their nakedness [i.e. genitalia] needs to be pressed against the ground or [they should be] sitting on another thing, because then their heart does not see their nakedness [genitalia]. Which is not [the case] with a man (Beit Yosef in the name of A"Ch) and see below Siman 96, S'if 3)
[For] the rest of one's body parts, seeing nakedness is permitted, but if any of one's body parts touches, whether it is one's own nakedness [genitalia] or one's fellow's nakedness [genitalia], it is forbidden to recite the Sh'ma or to pray [the Amidah]. And if his thighs [are such] that the nakedness [genitalia] is lying on them, then he needs to separate between them with a cloth or to distance them [i.e. the body parts] in such a way that the member does not touch them [the thighs].
If one's garment was wrapped around their waist to cover themselves from the waist down, even though from the waist up he is naked, it is permitted to recite the Sh'ma. But to pray [the Amidah] is forbidden until he covers his heart.