Możesz wziąć sweter z wełny, byleby zmechacenie było małe.

Byleby means as long as, provided that, or so long as.

In this sentence, it introduces a condition:

• Możesz wziąć sweter z wełny, byleby zmechacenie było małe.
• You can take the wool sweater, as long as the pilling is small / minimal.

It is a fairly common Polish way to express a condition, but it can sound a little more conversational than a very neutral option like jeśli or pod warunkiem że.

Compare:

• byleby było tanio = as long as it’s cheap
• byleby zdążyć = as long as we manage to make it in time

So the basic idea is: this is acceptable, but only on one condition.

After byleby, Polish often uses a verb form that looks like the past tense, even though the meaning is not actually past.

So:

• byleby zmechacenie było małe

does not mean as long as the pilling was small in a past-time sense. It means:

• as long as the pilling is small
• provided that the pilling be small

This is a special pattern used after words like byleby, żeby, aby, etc. It often expresses a wish, condition, or requirement rather than normal past time.

A learner-friendly way to think about it:

• jest = plain statement: it is
• było after byleby = conditional/required situation: as long as it is / provided it is

Because the subject is zmechacenie, and zmechacenie is a neuter noun.

So the agreement is:

• zmechacenie — neuter singular
• było — neuter singular past-form verb
• małe — neuter singular adjective

Polish adjectives and many verb forms must agree with the noun they describe.

Compare:

• Problem był mały. — masculine
• Plama była mała. — feminine
• Zmechacenie było małe. — neuter

So the form is determined by grammar, not by meaning.

Zmechacenie refers to the fuzzy, worn, pill-covered look that fabric gets after use. In English, this is usually called pilling or bobbling.

It comes from mech meaning moss or something soft/fuzzy, and the verb zmechacić (się) means to become fuzzy / to pill.

In clothing context:

• zmechacony sweter = a pilled sweater
• zmechacenie materiału = fabric pilling

So here zmechacenie było małe means the sweater should have only a small amount of pilling.

It is understandable, but it sounds a bit formal or technical.

In everyday Polish, people are often more likely to say something like:

• byle nie był bardzo zmechacony = as long as it isn’t very pilled
• byle był mało zmechacony
• o ile nie jest mocno zmechacony

Using the noun zmechacenie is possible, but many speakers would more naturally describe the sweater directly with the adjective zmechacony.

So your sentence is grammatical, but in normal conversation a Pole might prefer a version like:

• Możesz wziąć wełniany sweter, byle nie był bardzo zmechacony.

Wełny is in the genitive case.

The phrase z + genitive often means made of or from a material:

• sweter z wełny = a sweater made of wool
• stół z drewna = a table made of wood
• pierścionek ze złota = a ring made of gold

So:

• dictionary form: wełna
• genitive singular: wełny

That is why you get z wełny.

Be careful: z can also take the instrumental in other meanings, such as with:

• z kolegą = with a friend

But in the sense of made of, here it takes the genitive.

Yes. Both are correct.

• sweter z wełny = a sweater made of wool
• wełniany sweter = a wool sweater

The adjective wełniany is often the more natural, compact choice in everyday speech.

So these are both fine:

• Możesz wziąć sweter z wełny...
• Możesz wziąć wełniany sweter...

The difference is mostly stylistic:

• z wełny emphasizes the material a bit more
• wełniany is shorter and often sounds more idiomatic

This is about aspect, which is very important in Polish verbs.

• brać = imperfective
• wziąć = perfective

Here, wziąć is used because the sentence refers to a single complete action: taking the sweater.

• Możesz wziąć sweter. = You can take the sweater.
  • one completed action

If you used brać, it would sound less natural here, because brać usually refers to an ongoing, repeated, or more general process.

Compare:

• Możesz wziąć ten sweter. = take this one
• Możesz brać, co chcesz. = you can take whatever you want / you may keep taking

So in this sentence, the perfective wziąć is the normal choice.

It can suggest either, depending on context.

• can = ability
• may = permission

In this sentence, możesz wziąć sweter most naturally means you may take the sweater or you can take the sweater in the sense of permission/acceptability.

Polish móc often covers both ideas, and context tells you which one is intended.

So:

• Możesz to zrobić. = You can do it / You may do it
• Nie możesz wejść. = You can’t / may not come in

Here, because a condition follows (byleby...), the meaning is clearly about permission or acceptance:

• You can take it, provided that...

Because byleby introduces a subordinate clause.

Polish normally separates subordinate clauses with a comma, just like English often does with clauses introduced by provided that, if, because, and so on.

So:

• Możesz wziąć sweter z wełny, byleby zmechacenie było małe.

The comma marks the boundary between:

1. the main clause: Możesz wziąć sweter z wełny
2. the subordinate conditional clause: byleby zmechacenie było małe

This comma is standard and expected.

Małe literally means small, so zmechacenie było małe means the amount of pilling was small.

That is understandable, but Polish speakers might more often choose wording that sounds a bit more idiomatic, for example:

• niewielkie = slight / minimal
• mało widoczne = not very visible
• nieduże = not large

So you could also say:

• byleby zmechacenie było niewielkie

That may sound slightly more natural or polished than małe, because małe is very general.

Yes. If you want something that sounds more natural in everyday Polish, a native speaker might say:

• Możesz wziąć wełniany sweter, byle nie był bardzo zmechacony.
• Możesz wziąć sweter z wełny, o ile nie jest mocno zmechacony.

These versions avoid the noun zmechacenie and describe the sweater directly as zmechacony.

Your original sentence is grammatical and understandable, but these alternatives may sound more natural in conversation.