大部分病毒（如流感病毒等许多动物病毒）都拥有病毒包膜（英语：viral envelopes）结构，覆盖在衣壳的外面。病毒包膜物质通常源自于宿主的细胞膜（携带宿主的磷脂和蛋白质），但也包含有病毒的糖蛋白。病毒包膜帮助病毒躲避宿主的免疫系统的监视。包膜表面的糖蛋白可以用于识别并激活宿主细胞膜表面的受体，在病毒进入细胞后，病毒包膜会与宿主的细胞膜融合在一起，使得病毒的衣壳和基因组可以进入并感染宿主细胞。

The cell from which the virus itself buds will often die or be weakened and shed more viral particles for an extended period. The lipid bilayer envelope of these viruses is relatively sensitive to desiccation, heat, and detergents, therefore these viruses are easier to sterilize than non-enveloped viruses, have limited survival outside host environments, and typically must transfer directly from host to host. Enveloped viruses possess great adaptability and can change in a short time in order to evade the immune system. Enveloped viruses can cause persistent infections.

Most viruses (e.g. influenza and many animal viruses) have viral envelopes covering their protective protein capsids. The envelopes are typically derived from portions of the host cell membranes (phospholipids and proteins), but include some viral glycoproteins. They may help viruses avoid the host immune system. Glycoproteins on the surface of the envelope serve to identify and bind to receptor sites on the host's membrane. The viral envelope then fuses with the host's membrane, allowing the capsid and viral genome to enter and infect the host.