Paddy bought a thermos flask at Boots?

Paddy went in to Boots and was sold a Thermos flask, they told him it will keep his tea hot all day, or if he puts some thing cold in the flask it will stay cold all day. Next day at work on the building site he gets his flask out, his mates ask him what is it?he replies it will keep my tea hot all day, or if I put some thing cold in it will stay cold all day. ok they replied what have you got in your flask today? to this paddy replies two cups of tea and an ice cream