That's correct. It's generally recommended for lenses to have at least over 100 Dk/t for sleep and they need to be approved for that. Dk/t is the measured oxygen transmission through the lens material, the higher, the better. I would not recommend lenses with Dk/t of 30 and under even for daily wear as they starve eyes of oxygen. Especially since there are very affordable ones with very high Dk/t like Miru and Biofinity (around 160 iirc).