I bought my first 2 Silipint tumblers while on holiday in Lake George, NY at an Orvis store. I bought 2 of the green pint tumblers with the Orvis logo on them. I thought it was a novelty item at first but soon realized they were seriously durable and had good insulating properties. I went to the Silipint website and saw that lids were available. I wasn't sure how leak proof the lids would be since they are held in place by friction. The entire lid fits inside the walls of the pint. I filled it with water, plugged the mouth piece and straw hole, turned it upside down and not a single drop leaked out. The lid also adds some stability to the flex of the walls of the pint. The lid also adds to the insulation value. Keeps hot hot and cold cold for several hours. Easy to wash by hand or just put it in the dishwasher. Either way you have a well designed and engineered product that with nominal care will last for many years. It has become my favorite cold and hot beverage cup. Try it and you will love it.