What happens if you cast invisibility on a chest or closet that weighs no more than 100 lb./level and then put some items inside it (and close the door)?
What if you put a living creature and not items?
Does it matter if the creature is conscious or unconscious, willing or unwilling?
What if the items or creature are already inside the closet before you cast the spell?
These types of questions are pretty common. The rules are often unclear, IMO not necessarily because of inadequacies of the developers/writers, but because (as we see from the variety of answers/discussions) these are tough, complex questions. I don't have a definitive answer, but I have a recommendation that I believe warrants more than a comment, so I'll post it here:
Avoid trying to approach this as though you are an in-world physicist/alchemist/wizard. The dynamics of what "should" happen based on a particular in-game rationale or theory of magic are fascinating. If you were writing a novel where you have total control over the actions of characters, then you'd be fine. But in a gaming setting you'll be better served in the end by thinking like a game designer. In other words, what ruling will give me a house rule that
a) let's my players (and NPCs and monsters) do cool and interesting things,
b) doesn't hamstring the spell and make it useless, and
c) can be re-used consistently without unbalancing my game.
If being able to use invisibility on a roll of fabric, then wrap objects in it to make them invisible makes a 2nd level spell capable of rendering effects on par with a 7th Mass Invisibility spell, then you'll need to curtail that. Perhaps the invisibility magic struggles with the total weight obscured, not just the weight of the original container, so that once you add mass that exceeds the target 100 lb./lvl, the spell collapses.
The primary point is that whatever you decide to use, above all else the end result must be playable, both from the perspective of "players want to use it" and "DM can let them use it without the world unraveling". Your final rule may not fully satisfy certain "magi/engineer" types, but as the creator of your universe, sometimes you have to leave a bit of mystery in the world to keep it from flying apart. Sometimes, "No one knows, that's just the way this magic works" needs to be an acceptable answer.
"items picked up disappear if tucked into the clothing or pouches worn by the creature."
Based on the above, I'd say stuff put into the box arguably becomes invisible. A pouch is a container. A box is a container. Stuff put into an invisible container disappear.
Sure, the RAW says in the quote above that the container is "worn by the creature", but there's no creature when you cast the spell on a container itself... is there? Well, yes. But... a creature is a thing. A container is a thing. Invisibility turns things invisible... with a nice generalization, and perhaps considering that there's an ant inside / under the box "wearing" the box, you could... well, you get my drift.
All in all I'd say the rules aren't clear, so it's up to the DM.
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An important edit...
...regarding the supposed 100% clarity of the rules (as implied by the - since then possibly deleted - comments by KRyan and others.) Note the use of phrases like "the rules are unclear", "reasonable", "make an exception", etc., all implying that the RAW can be, and in the case of invisibility, is open to DM judgment (to a degree, at least), despite its perceived, but somewhat useless logical clarity. (Btw, would we need official clarifications, erratas, sites like this with questions like this, etc., if all the rules were crystal clear? ;)) Please, also note the source of the following quote.
The rules are unclear about exactly what happens to other creatures that you might hold or carry when you become invisible. In general, you should treat each creature as a separate individual when you consider how any spell or magical effect works. The invisibility and greater invisibility spells affect one creature only, as does a ring of invisibility (which works just like the spell). It's reasonable to make an exception for creatures you carry tucked into your clothing (or that you pick up and tuck into your clothing), and that can include a familiar, cohort, or animal companion if the creature is small enough to fit into your clothing.
– There, Not There (Part One) by Skip Williams on Wizards.com, 3.5 archive
Let me emphasize again: I think the best option is to go for a reasonable and useful interpretation deduced from the writers' intent (which does not necessarily equal a house rule, especially if/when the RAW is ambiguous.)
The box and its contents - creatures included - probably vanish from sight.
The author of the Invisibility spell description, it seems, had an oversight. At the beginning, they write:
The creature or object touched becomes invisible, vanishing from sight, even from darkvision.
... and then they proceed for the remaining paragraphs to describe the nuanced details of the workings of an invisible creature, ostensibly entirely forgetting to provide any similar level of detail on the topic of invisible objects - or, in fact, any information at all.
At the end they mention that objects can be made permanently invisible, but in addition to the fact that objects which cast light still do so despite being invisible themselves, that's about all we know on this topic.
The rules of D&D 3.5e are not exactly a model example of a complete and thorough rule set, so this is not totally surprising.
We can only really extrapolate from what happens to creatures: when they become invisible, any gear they're holding onto or wearing vanishes, and so does anything contained inside that stuff. Things contained inside the creature disappear, too, so we don't see the hovering contents of a digestive tract drifting through the air.
The closest parallel for an object would be this, I think: the object vanishes, and so does everything contained inside it. Anything that could be considered a part of that object, or an extension of it, vanishes too - the shade on a lamp vanishes just as the helmet on your head would, and coats hanging from a coat stand might vanish just like the key dangling from your finger would. Anything contained within those things - like a wallet inside one of those coat pockets - also vanishes.
So if you hid in an invisible box, you'd vanish from sight as well by the nature of being inside it.
If someone glances in such a way they happen to peek straight inside the box, then... I'm not sure. I'd imagine the parts of you not hidden behind the (presently invisible) walls of the box would show up, but that's just me. That might, by extension, mean that if you're standing in an invisible vase that comes up to just beneath your chin, people would just see your apparently disembodied head floating in midair.
The rules don't go into that detail, though. Perhaps they might've if it weren't for the apparent oversight.
if it is illusion magic, which creates a field of distortion that covers the object with what SEEMS to be behind it (a la IRL invisibility nanocamera cloak) then yes
if it is alteration magic, which physically alters the material properties of the object, rendering it transparent to visible wavelenths of light then no
The box becomes invisible.
This lets you see the creature inside it.
Personally, I would say the creature becomes invisible. In the spell's description, it says that if something were picked up by someone invisible and tucked under their shirt, then it would become invisible. While a different situation, I'd say it should apply the same way, as it's essentially the same principle. Based on the wording in the description, an apple being eaten would disappear-thus so would someone stored in an invisible box.
Remember - you can climb inside the large box and be invisible, but you cannot see what is happening outside the box. If there is an opening in the box, that opening is not invisible and so allows anyone outside to look into the box through the opening; just as you can look out through that hole.
If the box were prepared in advance to have a fine screen of holes, that combined with the relative darkness inside the box would protect against casual observation of the box, but not studied observation of the box. ie
Hey George! I think there's something inside the box moving around. Let's open it up and check it out.
The answer is YES.
Invisibility Lvl 3 Spell
"Items dropped or put down by an invisible creature become visible; items picked up disappear if tucked into the clothing or pouches worn by the creature."
Thus if you cast Invisibility on an item and then used a permanency spell on it; You could TUCK yourself into the container.
To see outside of the Box, I would build it to have a 1 way mirror as a surface. Thus allowing you to see out, but no one could see in.
Consider Harry Potter and his Cloak of invisibility... which was really a shroud. You could perma-invisibility a cloth shroud, made of a material you can partially see thru and then toss it over your head.
