This is the 17415th most frequent Russian word.
теплых
"Of warm" or "warm" (genitive plural or accusative plural, depending on context).
In this sentence, 'тёплых' describes the physical property of warmth inherent to the sweaters.
Я принёс несколько тёплых свитеров на случай холодной погоды.
I brought some warm sweaters in case of cold weather.
Here, 'тёплых' metaphorically describes the pleasant and warm atmospheric conditions of the days.
Она вспомнила о тёплых днях, проведённых на берегу моря.
She remembered the warm days spent by the sea shore.
This usage of 'теплыми' metaphorically describes the heartfelt and friendly feelings within a social setting.