and in destabilizing kinetic penetrators. Hardened steel plates have become commonplace for outer part of spaced armour from the 1980s, not only on tanks but also on APCs and IFVs. With this add-on armour, even the APC's thin armour is sufficient against kinetic bullets of 12.7 mm (Stryker and BTR-80 upgrades) and 14.5 mm (Bradley, BMP-3) and also provides some protection against IEDs. The increase in the number of layers in spaced armour increases the physical damage and destabilization of jets and kinetic penetrators, so it is common in more modern armour to use successive layers alternating between softer (air, aluminium or plastic) and harder (RHA, SHS) layers. With multiple layers the likelihood of a bounce in case of kinetic projectiles is also increased. Thus, later T-72B and T-90 armour used seven-layered spaced armour (with hardened steel plates) to achieve much stronger protection at a cost of minimal weight increases. The more advanced late Cold War tanks were given multi-layer skirts (Leopard 2), in which passive (or reactive) effects significantly reduced the effectiveness of HEAT ammunition. At the same time, these elements are already heavy and have considerable thickness, which increases the size and weight of the vehicle and make maintenance difficult. Russian and some Western tanks carry explosive-reactive armour blocks to increase the effectiveness of spaced armour (particularly in the case of side skirts, e.g. TUSK and T-90), and main frontal armour. Almost all modern Western and Japanese and most Soviet tanks used some kind of spaced armour on the fronts and sides. Side panels of superstructures usually contain fuel, batteries and other less vital elements or munition of secondary weapons, because they also reduce the effectiveness of penetrating projectiles. In the most important areas (frontal armour and sides of turret) the cavity of spaced armour contains composite panels. From the 1980s, most Western tanks have composite armour blocks on the frontal part of the skirts, made of hardened steel or NERA armour (non-explosive-reactive armour, known as "Burlinghton armour"). Most modern MBTs (e.g. T-72B, Leopard 2, M1, Type 10, K2, T-90, Type96) have NERA armour in their spaced armour which supplement the inner ceramic armour and spall liners in some cases. In contrast, Soviet tanks were initially made with ceramic (corundum or silicate) inserts (T-64A, T-72A, T-72M1, T-80) and NERA-style inserts spread in the upgraded versions of their vehicles later (T-72B, T-80A, T-72BU). More detail in composite armour. Currently,