left the one on the left in the melting snow, and apparently rival balls are similar to sponges. they are off brand so maybe that has something to do with it. :
Amazon.com: NERF Hyper Evolve-100 Blaster, 70 Hyper Rounds, Spring-Open Instant Reload Hopper, Up to 110 FPS Velocity, Eyewear Included : Toys & Games
Amazon.com: NERF Hyper Mach-100 Fully Motorized Blaster, 80 Hyper Rounds, Eyewear, Up to 110 FPS Velocity, Easy Reload, Holds Up to 100 Rounds
Nerf Hyper Rush-40, Siege-50 and Mach-100 review: where the rubber meets the foam - The Verge
Nerf reveals Hyper, its next-gen high-capacity blasters with the fastest reloads ever - The Verge
Amazon.com: NERF Hyper Rush-40 Pump-Action Blaster, 30 Hyper Rounds, Eyewear, Up to 110 FPS Velocity, Easy Reload, Holds Up to 40 Rounds : Toys & Games