Such is their value that criminal gangs scour the country at night stealing from clothes banks in highly organised operations.
A 'Prime Time' investigation showed just how much gangs are profiting, mainly at the expense of charities. A clothes bank generates, on average, an income of €8,164 a year and a profit of €7,103.
With more than 3,000 around the country, the profit could hit more than €21m every 12 months. And that doesn't take into account the thousands of bags collected directly from homes.
A huge market in second-hand clothes has emerged in countries such as Poland, Lithuania, Romania and further afield.
A 40ft-trailer full of clothes is worth between €35,000 and €100,000 in Eastern Europe. Cotton is the most valuable fabric.
Synthetics and wools are worth less and are generally recycled.
Depending on their quality, an average black bag of items can fetch between €30 and €40 in a shop.
Criminals are pretending to collect on behalf of charities and flogging the clothes in Eastern Europe. As part of the scam, bogus leaflets delivered to homes give the impression proceeds will be used for good causes. But they are costing Irish charities millions of euro every year.
Prime Time secretly recorded a van delivering leaflets to areas like Swords, Malahide Blanchardstown, Clonsilla and Castleknock in Dublin. A different leaflet was dropped into letterboxes every night.
"For every bag that's taken from us, it is worth anything from €30 to €300 in our shops, depending on the quality," Ann Kelly, of Enable Ireland, told the programme.
Vans were recorded arriving in a warehouse in Dublin Port where the clothes were dropped off and leaflets were collected. An undercover researcher was warned of the risks of getting involved in the racket.
"They can burn your van and everything, you know, it's not easy," an Eastern European man told him. A week later, the researcher returned with bags of clothes and was paid €107 for 107kg of items.
Stickers, some 500 of which cost just €6.50, claim the money made from the clothes goes to good causes, but it couldn't be further from the truth. Mobile phone numbers are provided but Prime Time found that no one was ever on the other end of the line. A leaflet that had been delivered to homes in north Dublin asked residents to fill bags provided "with all types of wearable ladies, gents, children's clothing, blankets, shoes, etc".
"All clothes are shipped to under-developed countries to improve their lives and welfare," it claimed.
Some organisations like the ISPCC have agreements with commercial operators to collect the clothes, with the charity receiving a percentage of the money made.
But criminal gangs are hitting legitimate collectors. One charity, Laois Autism, told of how its eight banks generated an income of €150 a week but, because of theft, the figure had fallen by two-thirds.
Footage from a surveillance operation carried out by Prime Time showed a gang breaking into one of the banks and taking all the clothes.
The sting revealed that three vans travelled from a location in Co Kildare every night, hitting locations across the country.
"We're being robbed blind," Brendan Dempsey of St Vincent de Paul in Cork told Prime Time.