noun
heat retention; thermal insulation; insulating property
Refers to the ability of a material or product (especially clothing, containers, or building materials) to keep heat from escaping. Often used in product descriptions.
このジャケットは保温性に優れている。
This jacket has excellent heat retention.
保温性の高い素材を使った水筒です。
It's a water bottle made of a material with high thermal insulation.
断熱性 is thermal insulation in a broader sense (preventing heat transfer), while 保温性 focuses on retaining heat inside.
Compound of 保温 (heat retention) + 性 (property, nature).