High Street food and drink chain Pret A Manger is to increase the discount for bringing in a reusable cup to 50p from the first week in January.
Since August, it has offered customers 25p off their coffee if they bring a reusable cup that it can be served in.
In the UK, it is estimated some 2.5 billion disposable coffee cups are thrown away every year.
In theory, they are "recyclable", but in reality, only a tiny percentage is dealt with sustainably.
For a cup to be recycled, it is first necessary to separate the inner plastic layer from the paper outside.
Pret said it had examined whether to charge customers for disposable cups.
"We debated whether charging people for using paper cups felt right.," said Pret chief executive Clive Schlee.
"We decided that it goes against our instincts as we would prefer to be generous to our customers than to tax them. Let's see what impact the new discount has."
Pret says that it is also going to "source a well-designed reusable cup, ready to launch later in 2018" and will explore making china cups more available in those stores which have seating.
Pret is owned by UK private equity firm Bridgepoint, which may float the firm on the New York stock exchange next year.
The UK Parliament's environmental audit committee earlier this winter considered the latest thoughts from campaigners and industry figures on how best to increase the number of disposable coffee cups recycled.
Meanwhile, many of the big names in takeaway beverages, including Caffe Nero, Costa Coffee, McDonald's, Pret A Manger and Starbucks, have signed up to a scheme to collect and recycle more of the current type of cups.