“ In straw, grape-skins, wool-flocks, or grass it is permitted, provided they are dry, but not when they are still wet.
GEMARA: A question was propounded: "Is the use of olive waste only prohibited, but the use of the oil-cakes allowed; or does the Mishna allude to oil-cakes and still more so to olive waste (for it produces more heat) ?" For the purpose of depositing in, both kinds are not allowed; (but if the victuals have been deposited in a permissible thing and were subsequently placed on oil-cakes no wrong was done, because) oil-cake does not produce heat; olive waste produces heat. ”

“ Said R. Jehudah in the name of Rabh: "It is R. Meir (of the Mishna, Kelim, VIII.) who holds that the attachment built on a hearth is on a par with the hearth itself and becomes unclean when touched by an unclean thing."
"When wet." A question was propounded: Naturally or artificially wet? Come and hear. The Mishna says: "Not with straw, nor with grape-skins, nor with wool-flocks, nor with grass when wet." It is right only if we accept the theory that they became wet, but should we venture to think them naturally wet, how is this to be imagined? Can wool-flocks be naturally wet? ”

“ R. Mordecai said to Rabha that R. Qatina has objected to the above rabbis, who said that if it were not replaced before Sabbath it must not be used, from a Mishna (Kilaim, I. 9) , which states plainly that it may be taken out on Sabbath. This question remains.
MISHNA IV.: (A vessel) not covered during daylight must not be covered after dark. If, after having been covered, it became uncovered, it is permitted to cover it again. A pitcher may be filled with cold victuals and put under a pillow (to keep it cool) . ”

“ Still Rabbi accepted his decision.
R. Na'hman said to his slave Doru: "Store some cold victuals for me and bring me warm water from a Gentile cook-shop." R. Ami heard this and was angry. Said R. Joseph: "What was the reason of his anger? Did not R. Na'hman act in accordance with the teachings of the great masters, Rabh and Samuel?" R. Jehudah in the name of Samuel said: It is permitted to store cold victuals, and R. Samuel b. R. Itz'hak said in the name of Rabh: Anything that may be consumed raw is not included in the prohibition relating to cooking by a Gentile ”