6LoWPAN defines how to carry Ipv6 packet over IEEE 802.15.4 low power wireless or sensor networks. Limited bandwidth, memory and energy resources require a careful application of Ipv6 in a LoWPAN network. The aim is to develop personal networks, mainly sensor based, that can be integrated to the existing wellknow network infrastructure by reusing mature and wideused technologies. IPv6 has been chosen as network protocol because its characteristics fit to the problematic that characterize LoWPAN environment such as the large number of nodes to address and stateless address autoconfiguration. However, an IPv6 header compression algorithm is necessary in order to reduce the overhead and save space in data payload. In fact, the IEEE 802.15.4 standard defines an MTU of 128 bytes that decrease to 102 bytes considering the frame overhead, a further reduction is due to the network and transport protocols frame overhead that, in case of Ipv6 and UDP, allow to carry only 33 bytes for application data. The aim of this work is to describe and compares the proposed Ipv6 header compression mechanisms for 6LoWPAN environments.