Hlau Hollow hlau cov qhov rooj yog ua los ntawm ntau yam ntawm cov cheebtsam. Ib qho ntawm cov feem tseem ceeb tshaj plaws yog cov khoom siv tseem ceeb. Ntawm no yog 5 ntawm cov qauv txheem cov hom siv hauv cov hlau wollow hlau:
1. Honeycomb
2. Polystyrene
3. Polyurethane
4. Hlau txhav
5. MInali Tub Ntxhais
