The incident happened at the Blacks store in High Street, Swansea, sometime between 5.30pm on Wednesday 13th February and 8am the following day.
At least 30 items of North Face clothing – including body-warmers, coats, lightweight jackets, fleeces and t-shirts worth thousands of pounds – were stolen.
Police are appealing for information about the burglary and issuing a warning that the goods may be offered for sale.
Sergeant Cheryl Griffiths of the Swansea city centre sector said: “It is highly likely that these items will be offered for sale illegally so if anyone is selling North Face clothing we want to hear about it.
“An investigation is underway and we are appealing to anyone who is offered this brand of clothing for sale or who has any knowledge of this incident to contact the police.”
Call police on 101 or Crimestoppers anonymously on 0800 555 111.