hot water registers

hello, i have a hot water furnace that heats my tap water and house, and

i replaced my heater covers with heavy duty polypropylene soffit, now i

did some research, the furnace water never goes above 160F, the water

registers never go above 100F, and the soffit is rated not to distort

until a temp above *. ever since i installed them, the home made soffit

covers only get warm,never hot no matter how long the furnace is

running, My question is, would this pass for a safe cover untill i can

afford store bought * thank you..