Dušek je u zaštitnoj foliji.

Dušek means mattress.

It is a very common everyday word. In some regions, you may also hear madrac, which also means mattress. Both are used, but dušek is very natural in speech.

Serbian has no articles, so there is no separate word for a / an / the.

So Dušek je u zaštitnoj foliji can mean:

• The mattress is in protective foil
• A mattress is in protective foil
• The mattress is wrapped in protective film

The exact meaning depends on context.

Je is the 3rd person singular form of the verb biti (to be).

So:

• dušek = mattress
• je = is
• u zaštitnoj foliji = in protective foil / film

Literally: Mattress is in protective foil.

Because the preposition u here means in, expressing location, and that requires the locative case.

So zaštitna folija changes to zaštitnoj foliji in the locative singular:

• zaštitna folija = protective foil / film
• u zaštitnoj foliji = in protective foil / film

Both the adjective and the noun change to match the case:

• zaštitna → zaštitnoj
• folija → foliji

The preposition u can take different cases depending on meaning.

Here are the two most important uses:

• u + locative = in, inside, at a place
  
  • u sobi = in the room
• u + accusative = into a place, showing movement/direction
  
  • u sobu = into the room

In Dušek je u zaštitnoj foliji, the mattress is already located there, so Serbian uses u + locative.

Zaštitna folija means protective foil, protective film, or sometimes protective wrapping, depending on context.

In this sentence, it most likely means the mattress is still covered in some kind of protective plastic packaging.

• zaštitna = protective
• folija = foil / film / thin wrapping material

In natural English, this might be translated more smoothly as:

• The mattress is in protective plastic.
• The mattress is wrapped in protective film.

Literally, u zaštitnoj foliji means in protective foil.

In real usage, this usually implies wrapped in or covered in protective foil/plastic. Serbian often uses u this way for packaging or covering.

So even though the literal meaning is in, the natural meaning is often:

• The mattress is wrapped in protective foil.

Yes. Some common alternatives are:

• Dušek je umotan u zaštitnu foliju.
  = The mattress is wrapped in protective foil.

• Dušek je zapakovan u zaštitnu foliju.
  = The mattress is packaged in protective foil.

• Dušek je u foliji.
  = The mattress is in foil / wrapped in foil.

The original sentence is short and natural, especially if the situation is obvious.

In Serbian, adjectives usually come before the noun, just like in English.

So:

• zaštitna folija = protective foil
• u zaštitnoj foliji = in protective foil

The adjective must also agree with the noun in:

• gender
• number
• case

Since folija is feminine singular and here in the locative, the adjective becomes zaštitnoj.

A rough pronunciation guide:

• Dušek ≈ DOO-shek
• je ≈ yeh
• u ≈ oo
• zaštitnoj ≈ ZAHSH-teet-noy
• foliji ≈ FOH-lee-yee

A full rough pronunciation: DOO-shek yeh oo ZAHSH-teet-noy FOH-lee-yee

A few useful sounds:

• š sounds like sh in shoe
• j sounds like y in yes
• č / ć are different sounds in Serbian, but they do not appear in this sentence

Yes, Serbian word order is more flexible than English word order.

The neutral version is:

• Dušek je u zaštitnoj foliji.

But depending on emphasis, you might also hear:

• U zaštitnoj foliji je dušek.
  = It is the mattress that is in protective foil.

• Dušek u zaštitnoj foliji je...
  = The mattress in protective foil is...

Still, for a basic statement, Dušek je u zaštitnoj foliji is the most straightforward.

The dictionary forms are:

• zaštitni / zaštitna / zaštitno = protective
• folija = foil, film

Together in dictionary form:

• zaštitna folija

In the sentence, they appear in the locative singular:

• zaštitnoj foliji

Not always exactly.

Serbian folija can refer to several thin sheet-like materials, depending on context, such as:

• plastic film
• wrapping film
• foil
• protective covering

So in this sentence, protective film or protective plastic wrapping may be more natural than the narrow English word foil. The best translation depends on the real object being described.