Do not buy from Smartwool. DO NOT BUY FROM SMARTWOOL!
Do not buy anything from Smartwool. That is the only advice you need to take from this and other reviews.
AVOID, AVOID, AVOID.
Smartwool pretends to be a UK-based company. They say they are Smartwool UK. They sell through a .co.uk website. Goods are priced in UK £. But in fact they are located in Italy. It's bordering on a scam.
The goods are despatched from Italy. And if you need to return anything - which you probably will as the sizing of their clothing is not great and the quality no more than average - that's when your nightmare begins.
You have to arrange shipping to Italy as if you are an exporter. You have to prepare complex documentation, including commercial invoices for Customs, as well as specific packaging materials for Customs to open/close. And of course, it's more expensive - maybe 3x the cost of shipping within the UK.
The 'importer' named on the documents is not even Smartwool but some Italian import agency. The email address given for them by Smartwool does not work - it doesn't exist.
Then their chosen delivery partner, UPS, kicks in. They will find something wrong with the Customs documents, even if there isn't, and UPS in turn prove to be hopeless and difficult.
So you contact Smartwool 'UK' customer service. You won't get a response. I sent multiple emails over a stressful 3-week period. Not a single response. They are uncontactable. You might notice they don't respond on here to reviews.
In desperation I contacted Smartwool in the US. Smartwool is an American company and I thought maybe they could force Smartwool Italia to respond. But no, they say they are nothing to do with them, even though they own the company.
Like I said, do not buy from Smartwool unless you want a nightmare like I had. Just avoid altogether.