Choosing to use that or which when they are part of an adjective clause is decided by a fairly simple rule, which if you do not know, can lead to a whole lot of confusion.  You use that before a restrictive clause, and you use which before everything else.

That or Which Rules

 Restrictive Clause – THAT

THAT is used before a restrictive clause.  What is a restrictive clause?
This is a part of the sentence that if it was omitted the sentence would lose its meaning.  it is a necessary part of the sentence.
“The painting that was in the bedroom was stolen.”
In this sentence, the use of THAT suggests that we own more than one painting, and we are talking about the particular painting that hung in the bedroom. If we do not use that with the adjective clause, we are do not make our meaning clear, which is that we own more than one painting and only the one that was in the bedroom was stolen.
Note that you do not need to use commas around the adjective clause when you use that.

Non-restrictive Clause—WHICH
A non-restrictive clause is something that, if you exclude from the sentence, does not alter the meaning of the sentence.  You are just adding additional information.
“The painting, which was in the bedroom, was stolen.”
What we mean when we say this is that the painting, which we had in the bedroom and which was stolen, was the only painting we owned. We are just adding the fact that it was our only painting. Note that commas are used when we preface the clause with which. In other words we could exclude that clause and the meaning of the sentence i.e. we had our painting stolen, is not altered in any fundamental way.

In both cases, the adjective clause tells us something about either the painting, but the choice of that or which changes the way we should read each sentence.

That and which differ in that which is a non-restrictive (nonessential) clause and that is a restrictive (essential) clause. Non-restrictive clauses are separated within the sentence by commas.  If the clause is in the middle of a sentence, a pair of commas marks the beginning and the end of the clause. A single comma is used when the non-restrictive clause is at the end of a sentence.
I wore a brand new dress, which I wore to the meeting.

That and which differ in that which is used in a non-restrictive (nonessential) clause and that is used in a restrictive (essential) clause.