The castelli undersaddle xl saddlebag features a taped zip seam to avoid rain and wheel spray from seeping in especially if you are using the saddle bag during the winter months its big enough to house multiple spare tubes a multi tool tyre levers an inflator co2 canisters some patches and also allow you to store a mini pump externally in an elasticated mesh sleeveon the underside of the bag if you ride like the pros youll be able to fit a 23 tubular tyre multitool a co2 canister a