Probably the most significant hurdle for hydrogen vehicles is storing sufficient hydrogen onboard. Three viable technologies for storing hydrogen fuel on cars are: compressed gas, metal hydride adsorption, and cryogenic liquid. However, each of these has significant disadvantages: volume, weight, boiling losses, or energy to compress or liquefy the hydrogen. Insulated pressure vessels can reduce these problems for hydrogen-fueled light-duty vehicles. Insulated pressure vessels can be fueled with liquid hydrogen (LH2), with low-temperature (80 K) compressed hydrogen (CH2) or with ambient-temperature CH2. In this analysis, hydrogen venting losses are calculated for insulated pressure vessels fueled with LH2 or with low-temperature CH2, and the results are compared to those obtained in low-pressure LH2 tanks. Hydrogen losses are calculated as a function of daily driving distance during normal operation, as a function of time during long periods of vehicle inactivity and as a function of initial vessel temperature during fueling. The number of days before any venting losses occur is also calculated as a function of the daily driving distance. The results show that insulated pressure vessels with packaging characteristics comparable to those of conventional, low-pressure LH2 tanks (low weight and volume), have greatly improved dormancy and much lower boil-off. Insulated pressure vessels used in a 17 km/l (40 mpg) car can hold the hydrogen indefinitely when the car is driven at least 15 km/day in average. Nearly all cars are driven for greater distances, so most cars would never need to vent hydrogen. Losses during long periods of parking are also relatively small. Due to their high-pressure capacity, these vessels would retain about a third of their full charge even after a very long dormancy, so that the owner would not risk running out of fuel. If an insulated pressure vessel reaches ambient temperature, it can be cooled down very effectively by fueling it with LH2 with no losses during fueling. The vessel has good thermal performance even when inexpensive microsphere insulation is used. Finally, the vessel eases fuel availability and infrastructure requirements, since it would be compatible with both compressed and cryogenic hydrogen refueling.