Are they leakproof?

No. Active Sipper, Active Swig, Active Gulp, Active Slurp, Popper Cap, Nomad Slid, Nomad Flipper and Nomad Bottle Straw Cap is splash-resist while Active Series Insulated, Standard Series Insulated cap, Standard series insulated cap and Nomad series Dual cap are not 100% leak-proof if jostled or knocked over and might resulting in some liquid spill out due to pressure released inside.