Wikia

The QuantumSuit Boots are a type of armor introduced by IndustrialCraft. They are extremely powerful, but also extremely expensive, requiring two Iridium Plates for crafting. Charged Boots allow the user to jump extremely high (up to 9 blocks up) when holding the 'Boost' key (defaults to ctrl) and prevent almost all fall damage (extremely high falls still cause death). Like the rest of the Quantum Armor it does this by reducing the stored EU before hurting the player, technically creating a forcefield of EU.

The QuantumSuit Boots, like all other pieces of the QuantumSuit, store up to 1,000,000 EU, and can only be charged in an MFSU, HV Solar Array or Charging Bench MK3. Because of the vast quantity of EU able to be stored by the QuantumSuit Boots, it makes it close to impossible for it to run out of charge (unless fall damage from extreme heights is taken), much like the rest of the QuantumSuit Armour (excluding the Quantum Helmet due to large amount of power being used to keep the player from starving or drowning). When you press the CTRL button with charged Quantum Boots you will be able to jump higher.