the technical specification:
JM series insulation brick

Items	JM23	JM26	JM29	JM32
Max service temperature C	1260	1400	1550	1650
Bulk density g/cm3 max	0.6	0.9	1.1	1.15
Cold crushing strength Mpa min	1	1.5	3.5	4.5
P.L.C 24hrs % max	±1.5 1250C	-0.7 1350C	-0.7 1450C	±0.5 1550C
Thermal conductivity w/m.K max
400C	0.20	0.28	0.4	0.65
600C	0.25	0.30	0.4	0.65
800C	0.30	0.42	0.45	0.60
1000C	0.35	0.50	0.55	0.65
1200C	0.40	0.55	0.60	0.65
Al2O3 % min	35	55	55	72
Fe2O3 % max	1.0	1.0	1.0	1.0
SiO2 % max	--	40	40	26