A flexible yet durable roll-down curtain is normally stored m a rolled condition, and is unrolled during use. The curtain includes plural, vertically spaced apart rods extending through a width of the curtain. When rolled, the curtain wraps around an elongate, spring-loaded mandrel assembly. The mandrel assembly couples with a pair of mounting brackets mounted at opposing sidewalls of a temperature- controlled compartment, A pair of locking brackets disposed directly opposite one another at opposing sidewalls engage opposing ends of a rod extending through the curtain, to retain the curtain in a deployed position. A flexible side seal provides a sealing engagement vertically along each side edge of the curtain. When deployed, the curtain extends from ceiling to floor, and from sidewall to sidewall, forming a barrier against uncontrolled air movement from a space on either side of the curtain to a space on an opposing side of the curtain.