Constance Marten and Mark Gordon used sleeping bags meant for summer while off-grid with their baby during winter, a court has heard.
Marten, 37, and Gordon, 50, are accused of the manslaughter of their daughter Victoria.
The Old Bailey has heard how the couple went to the south coast in early 2023 to avoid their fifth child being taken into care amid a high profile police hunt for the missing baby.
On Wednesday, jurors heard evidence from a chartered ergonomist who conducted experiments on the risk of hypothermia to Victoria.
Professor George Havenith, from Loughborough University, examined conditions as the defendants travelled to the South Downs and inside the tent once there.
Marten and Gordon purchased two Pro Action sleeping bags from Argos, the court was told.
Prof Havenith said the sleeping bags were not designed to be used in the UK countryside in January.
He added: “They were summer bags. They are for camping on warm summer nights or children’s sleepovers indoors.”
The prosecution allege Victoria died from hypothermia or was smothered while co-sleeping in the “flimsy” tent on the South Downs, despite past warnings.
It is alleged Victoria was inadequately clothed in a babygrow and that Marten had got wet as she carried the baby underneath her coat.
The child’s body was discovered with rubbish inside a shopping bag for life in a disused shed near Brighton after the defendants were arrested on February 27 2023.
Prof Havenith told jurors his experiments took account of the temperatures between January 8 and 10 2023, as well as the impact of wind and moisture.
As well as conditions inside and outside the tent, he also examined the micro-climate between layers of clothing worn by Marten, the court was told.
Prof Havenith said the micro-climate under Marten’s coat was “definitely not a safe environment”.
He added that the coat was “oversized” and there was “a substantial air layer around the baby that is easily disturbed”.
Asked about his overall conclusions, Prof Havenith said: “Baby Marten, in the conditions stated, especially where moisture was present in the clothing both in the tent and on the way to the South Downs, would have been exposed to substantial climatic cold stress which would have led to a substantial risk of hypothermia.”
Marten and Gordon, of no fixed address, have denied the gross negligence manslaughter of their daughter and causing or allowing her death between January 4 and February 27 2023.
The trial continues.