～した/～していた
（on the moutain）徐々に暖かくなってきたので、着たジャケットを脱いだ。
It means "I took off the jacket that I put on right now/a second/minutes ago because it was getting warmer and warmer".
I corrected "着た" into "着ていた".
In Japanese
～した is the simple past tense：着た, 見た, 買った, 走った, 歩いた...etc
～していた is the past progressive tense or the past perfect progressive tense：
着ていた, 見ていた, 買っていた, 走っていた, 歩いていた...etc
When we read "着ていたジャケット", it sounds like you put the jacket on a long time ago and was still wearing it when you said the phrase.
(We don't know when you put it on.)
If the member had written the mistaken phrase along with the time or another phrase, It would become a good phrase like this.
・１時間前に着たジャケットを脱いだ。
・山を登り始める時に着たジャケットを脱いだ。
In this case, do not write "1時間前に着ていたジャケットを脱いだ".
(I didn't put a comma after １時間前に on purpose.)
First, this phrase doesn't go well with this situation. Second, this means "I took off the jacket one hour ago" or "I took off the jacket that I was wearing until one hour ago".
The second phrase is very strange because you took off the jacket that you were not wearing. lol
It's really hard to explain the nuance. I tried giving an example, but I couldn't because
the best phrase depends on the situation, I couldn't give you all of the situations.
