Using someone’s item without permission:
It is forbidden for one to use an item that belongs to one’s friend without his permission. This applies even if one only plans to use it on a mere occasion. It is thus forbidden for one to visit his friend’s house in order to use an item of his without his permission even on mere occasion.
One knows for certain that the owner is not particular: If one knows for certain that the owner is not particular against one using his Sefarim, then it is permitted to use it without his explicit permission.
Items that people are not generally particular against being used: Those items in which it is not common at all for any people to be particular against someone using without their permission, such as items that do not receive any loss or damage at all through being used, it is permitted to use these items without permission. However, those items which minorities of peoples are particular against them being used by others due to worry of damage, then it is forbidden to be used without permission even if majority of people are not particular. This applies even if one is positive that no damage will occur to the item at all, it is nevertheless forbidden to borrow without permission.
May one use someone’s pen without permission?
May one use someone’s phone without permission?
May one borrow a piece of paper from a friend without permission?
May one use a hotel’s swimming pool without permission?
 Admur O.C. 14/10 and C.M. Metzia Upikadon 27 regarding Sefarim; Sheila Vesichirus 5 that it goes without saying that this applies to other items of Reshus; Rama O.C. 14/4; Smeh C.M. 75/6; Nimukei Yosef Tzitzis 12a in name of Ritva; See Piskeiy Teshuvos 14/10
 The reason: As the owner of the Sefarim suspects that perhaps he will spend a long time reading from it to the point that they will tear due to over usage, and therefore he is not pleased with allowing another to read from it at all. [Admur ibid; Nimukei Yosef Tzitzis in name of Ritva]
 Admur ibid; M”A 14/10
 Admur Sheila Vesichirus 5; Rama C.M. 292/20 regarding Pikadon of Sefarim by Talmid Chachaim; Smeh 292/45
 Admur Sheila Vesichirus 5; Shita Mekubetzes Baba Metzia 22b
 The reason: Although majority of people are not particular due to that chance of damage is very rare, nevertheless, we do not follow the majority in this regard to say that one can assume that this owner is not particular against it being used. [Admur ibid]
 Admur ibid and C.M. Metzia Upikadon 27 in parentheses regarding Sefarim
The reason: As nevertheless, the owner of the item suspects that perhaps it may get damaged, and thus if he knew that this person was using his item, it is possible that he would be particular, and it is thus found that he has borrowed without permission of the owners [Sheol Shelo Midaas], which is considered stealing, even if one causes no damage or loss to the item at all, as explained in Hilchos Metzia Upikadon 27. [Admur ibid; Metzia Upikadon ibid in parentheses]
 See Gr”a C.M. 163; Minchas Yitzchak 7/130; Piskeiy Teshuvos 14/10; See Chesed Lealafim 14/5, brought in Kaf Hachaim 14/31, for a similar defense regarding Siddurim; Lehoros Nasan 6/127-128