If his glucose levels are ok throughout the night, then maybe try getting him to use just a sheet and no duvet.
My husband has night sweats and this has helped him immensely, among a few other things:
- just underwear to bed, no pajamas
- no socks (this is very important)
- Pillow protectors on all the pillows (the kind for allergies)
- sleeping only with a soft, cotton percale bedsheet
- no sweets or heavy food right before bed. This sometimes triggers strange dreams for him, which was him to sweat
We also keep the house at 17 or 18 degrees at night, which helps. I got used to it, and prefer it this way now. Especially since I sleep with a huge duvet on my side