Bag of holding

(
Name	bag of holding
Appearance	bag
Base price	100 zm
Weight	15
Material	cloth
Monster use	Will not be used by monsters.

A bag of holding is a tool that appears in NetHack. Placing items into a noncursed bag of holding reduces their weight, making it one of the most coveted objects for general use.

Generation

The prize at the end of Sokoban always has a 50% chance of being a bag of holding, and will otherwise be an amulet of reflection.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Both prizes are no longer equally likely for each floor. Instead, floor 4a has a 75% chance for a bag of holding, and 4b has a 75% chance for an amulet of reflection.

Weight change

The weight of a bag of holding, including the 15 aum for the bag itself, depends on the weight of its contents ($cwgt$) and its BUC:

BUC	total weight
blessed	$15 + (\frac{cwgt}{4} + 1)$
uncursed	$15 + (\frac{cwgt}{2} + 1)$
cursed	$15 + (cwgt \times 2)$

Generally speaking: bags of holding halve the weight of its contents, blessed bags divide it by four, and cursed bags double it.

Putting dangerous items into bags of holding

Some items should not be put in a bag of holding - the following items will make the bag explode when placed inside, destroying all of its contents along with the bag:

• Other bags of holding
• Bags of tricks with charges remaining
• Wands of cancellation with charges remaining
• Other bags containing any of the above items
  • These have a chance of not exploding if you nest them - see below in "Nesting bags of holding".

The first two are straightforward to avoid; the wand can be trickier. To be safe, do not put any unidentified wands inside the bag that make engravings disappear (this includes cancellation, teleportation, and make invisible).

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Blowing up a bag of holding in this manner now scatters its contents instead of destroying them - this will break fragile items. If you had put in another bag of holding, its contents are also scattered, unless that bag was inside a non-magical bag, in which case it is destroyed.

Strategy

Bags of holding are possibly the highest-priority item for blessing in the game. A cursed bag of holding not only doubles the weight of its contents, but attempting to remove items from a cursed bag of holding may make them vanish, with a separate 1/13 chance for each item. In addition to doubling the amount you can carry in it without being encumbered, blessing also adds a layer of 'protection' from being cursed, e.g. via the curse items monster spell.

However, a bag of holding does not protect its contents from getting wet - to protect against this, you can apply grease to the bag or place it in a non-cursed oilskin sack to protect it from water damage.

Item management

Due to the risks of losing your most valuable items if your bag is cursed or else explodes, it is ideal to carry an additional bag around - a plain sack is usually enough for this purpose. The sack can be used to hold items that are rare or hazardous to a bag of holding - many players name this bag something like "Cancel" or "Don't ever put this in BoH!" and keep wands of cancellation and other precious items such as artifacts or a wand of wishing inside as a safety measure. Item management, such as handling stashes, becomes much less tedious if you carry around a second sack, letting you more efficiently sort through your possessions.

A spare sack can additionally serve as a "barrier" against curses if the bag of holding is placed inside, and keeping valuable and/or heavily used items in a separate bag makes theft (e.g., by the various nymphs) or destruction via lightning bolts, trapped boxes and the like much lesser dangers. As such, consider putting your bag(s) of holding into a sack on lower levels when not in use, especially once the Wizard of Yendor starts after you.

Handling cursed bags

If you find a bones pile with a bag of holding, it will probably be cursed and too heavy to lift. If you can still pick it up, then it can be uncursed with a potion of holy water or the scroll or spell of remove curse. Otherwise, the best solution in general is to zap it with a wand of cancellation - the beam will only affect the bag and simply sets it to uncursed.

You can also allow a gelatinous cube to eat the bag: the contents, even the organic ones, will land safely on the ground when you kill the cube. Just make sure you can secure all the items before they are damaged - and only do this if you have no need for the bag itself.

If cancellation is not available and the bag is too heavy to lift, you can #tip the bag as a last resort. This will still make items vanish, but at least you can get everything else out without being limited by your inventory.

Nesting bags of holding

It is possible, though risky, to first put items that would ordinarily cause a bag of holding to explode into sacks or oilskin sacks and then place them inside the bag of holding, without causing an explosion.

In general, two nested bags of holding at most are useful - the payload is limited by your ability to lift the innermost bag, not by the outermost weight, and you risk an explosion every time you add contents.

The chance of an explosion occurring then depends on the amount of nesting:

Number of sacks	Odds of explosion	Success probability
0	1/1	0
1	2/2	0
2	3/4	0.25
3	4/8	0.5
4	5/16	0.6875
5	6/32	0.8125
6	7/64	0.890625
7	8/128	0.9375
8	9/128	0.9296875
n, where n>6	(n+1)/128

If they do not explode, the effect of the two bags will be cumulative, as expected: if both are blessed, any items in the innermost bag will have their weight reduced to about 1/16.

As can be seen in the table above, nesting bags of holding with more than 7 sacks in between makes explosion more likely, so there is no point in using more than 7 sacks.

You may choose to continue to nest the bags of holding further; the chance of success with certain configurations of sacks between the bags of holding is given below:

Number of bags of holding	Sack spacing	Success probability
2	7	0.9375
3	7,7	0.769042...
4	7,7,7	0.512570...
5	7,7,7,7	0.256222...
6	7,6,6,6,7	0.0935839...
7	7,6,5,5,6,7	0.0236287...
...
43	3,2,2, ... ,2	very small

For example, if you use 7 sacks between each of three bags of holding like this (H for bag of holding, s for sack): HsssssssHsssssssH (denoted as "7,7" in the table above), the chance of successful nesting would be 1-(8/128) for the first nesting, and then (1-(8/128)) * (1-(16/128)) for the second nesting (each of the two 'inner' bags of holding put into the outermost bag must pass its own independent roll for the nesting to succeed) giving roughly a 23.1% chance that something will explode.

Some players either consider the 6.25% chance of explosion from nesting to be an acceptable risk, or assume from a test in wizard mode that it is safe. If you are confident you can withstand the explosion, you can risk it before you leave the main dungeon to increase your score or bring specific items to the ascension bar.

Messages

An <object> has vanished!

You applied or #looted a cursed bag of holding, causing items to disappear.

Variants

In SporkHack and UnNetHack, an exploding bag of holding scatters its contents nearby, rather than destroying them. In xNetHack, ¹⁄₁₃ of the contents are destroyed, and the rest are scattered.

In AceHack and NetHack 4, placing a charged wand of cancellation in a bag of holding causes the wand to become canceled; the bag and its other contents are unaffected.