Material compressibility and entropy is of great significance for inertial confinement fusion research. Preheat induced degradation on material compression under double shock compression is studied on ShenGuang series laser facility. The deviations on rear surface expansion and multiple shock timing are contrasted under different picket power. The measured preheat besides shocks could provide more physical boundaries and benchmarks from experiment. 1% silicon dopants is mandatory to keep ablator/fuel interface stable with and in a double-shock compression. While pure GDP ablator is applicable to . This study demonstrates a new testbed to provide in-situ preheat evaluation for implosion experiment. It aims to validate the preheat level and effects on material compression for a double shock, low convergence ratio design. It could also provide valuable information for target dopant design and upcoming shock tuning process.