JM R-38C Unfaced Fiberglass Batt Insulation
JM (Johns Manville) R-38C unfaced fiberglass batt insulation helps reduce heat transfer and improve sound control in wood-framed cavities. Made with long, resilient glass fibers and a formaldehyde-free binder, its designed for use in attics, walls, floors, ceilings, basements, and crawlspaces.
Key Features:
- High R-Value Performance: R-38C thermal resistance helps improve comfort and energy efficiency in demanding assemblies.
- Formaldehyde-Free Binder: Designed not to off-gas formaldehyde in the indoor environment.
- Unfaced Batt Design: No kraft facing/vapor retarderideal where a separate vapor control strategy is used or for layering over existing insulation (where allowed).
- Durable Fiberglass Construction: Inorganic glass fibers resist rot and mildew and wont corrode pipes, wiring, or metal components.
- Sound Control Benefits: Helps reduce sound transmission through wall and floor/ceiling assemblies.
Specifications Table:
| Specification | Details |
| Brand | JM |
| Manufacturer | Johns Manville |
| Product type/category | Batt Insulation |
| Material | Fiberglass |
| Facing | Unfaced |
| R-Value | R-38C |
| Width | 15-1/2 in |
| Length | 48 in |
| Thickness | 10-1/4 in |
| Coverage | 41.33 sq-ft |
| For use with | Wood stud framing |
| Application | New construction and remodels; walls, floors, ceilings, basements, attics, and crawlspaces |
| Flame spread index | <25 |
| Smoke developed index | <50 |
| Water vapor sorption | <5 % |
| Standards/Certifications | ASTM C665 Type I; ASTM E136; IBC; Energy Star Certified; Greenguard Gold Certified; Indoor Air Quality Certified; NAIMA 16 CFR Part 460; Recycled Content Certified |
| Product features | Formaldehyde-free; thermally efficient; sound control; durable inorganic glass (wont rot/mildew/deteriorate and is non-corrosive); dimensionally stable (wont slump/settle/break down in normal applications) |
| Manufacturer part # | U1347 |
Frequently Asked Questions (FAQ):
Q: What spaces is this batt insulation designed for?
A: Its intended for new construction or remodels in walls, floors, ceilings, basements, attics, and crawlspaces, and for use with wood stud framing.
Q: What does unfaced mean?
A: Unfaced batts do not include an attached vapor retarder facing; vapor control (if needed) is handled separately based on the assembly and local code.
Q: What are the batt dimensions and thickness?
A: Each batt is 15-1/2 in wide x 48 in long and 10-1/4 in thick (R-38C).
Q: Does it help with indoor air quality?
A: Its listed as formaldehyde-free and includes certifications such as GREENGUARD Gold and Indoor Air Quality certifications (per provided product data).
Q: Will it sag or settle over time?
A: The bonded glass fibers are described as dimensionally stable and designed not to slump, settle, or break down during normal applications.
Quiet Luxury, Hidden in the Walls
The most elevated rooms have a secret: comfort you cant see, but you feel immediately. This unfaced fiberglass batt brings a soft hush and steady warmth to walls and ceilings, supporting a calmer, more composed interior. I love it for spaces where you want performance without visual intrusionlayer it thoughtfully in attics and framed cavities, then let your finishes take center stage. Its the kind of behind-the-scenes essential that makes everyday living feel unmistakably luxe.
Upgrade your homes comfort and quiet with JM R-38C unfaced fiberglass batts designed for high-performance wood-framed spaces.
